Patent Publication Number: US-2021161511-A1

Title: Ultrasonic diagnostic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-217150, filed on Nov. 29, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     An embodiment disclosed in the present specification and drawings relates to an ultrasonic diagnostic apparatus. 
     BACKGROUND 
     In the medical field, an ultrasonic diagnostic apparatus is used for imaging the inside of a subject using ultrasonic waves generated by multiple transducers (piezoelectric vibrators) of an ultrasonic probe. The ultrasonic diagnostic apparatus causes the ultrasonic probe, which is connected to the ultrasonic diagnostic apparatus, to transmit ultrasonic waves into the subject, generates a reception signal based on a reflected wave, and acquires a desired ultrasonic image by image processing. 
     There are some methods of generating an ultrasonic image in the ultrasonic diagnostic apparatus. In the first method, a radio frequency (RF) signal, which is a reception signal, is delayed and added, a quadrature detection (demodulation) is performed, and a conversion to an I/Q signal composed of an “I (In-phase)” signal and a “Q (Quadrature-phase)” signal is performed. In the second method, a quadrature detection of an RF signal is performed, an I/Q signal is converted to baseband, and a delay addition is performed. The former method is also called “RF beamforming”. The latter method is also called “I/Q beamforming”. Functions for improving the image quality of an ultrasonic image in the I/Q beamforming include a function of controlling a gain of an amplifier, a function of controlling a reception delay curve of a delay control circuit, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration of an ultrasonic diagnostic apparatus according to a first embodiment. 
       Each of  FIGS. 2A and 2B  is a conceptual diagram for explaining a target frequency characteristic having the substantially flat bandwidth close to a designed frequency characteristic in the ultrasonic diagnostic apparatus according to the first embodiment. 
       Each of  FIGS. 3A to 3E  is a conceptual diagram for explaining a method of setting a reception filter in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 4  is a block diagram showing a configuration of a receiving circuit provided in a transmitting/receiving circuit in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 5  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the first embodiment as a flowchart. 
         FIG. 6  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the first embodiment as a flowchart. 
       Each of  FIGS. 7A and 7B  is a diagram showing a complex reception filter of the region of interest in the ultrasonic diagnostic apparatus according to the first embodiment. 
       Each of  FIGS. 8A and 8B  is a diagram showing a complex reception filter of each region of interest in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 9  is a diagram showing, as a frequency characteristic, an effect acquired when a complex reception filter is applied to an I/Q signal in a predetermined region of interest in the ultrasonic diagnostic apparatus according to the first embodiment. 
       Each of  FIGS. 10A and 10B  is a diagram showing an effect acquired when a complex reception filter is applied to an I/Q signal in a predetermined region of interest as an ultrasonic image in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 11  is a diagram for explaining a frequency compound in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 12  is a diagram showing a method of selecting a predetermined region of interest from set multiple regions of interest of the same depth in the ultrasonic diagnostic apparatus according to the first embodiment. 
         FIG. 13  is a schematic view showing a configuration of the ultrasonic diagnostic apparatus according to a second embodiment. 
         FIG. 14  is a block diagram showing a configuration of a transmitting/receiving circuit of the ultrasonic diagnostic apparatus according to the second embodiment. 
         FIG. 15  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the second embodiment as a flowchart. 
         FIG. 16  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the second embodiment as a flowchart. 
         FIG. 17  is a diagram showing an example of a shallow determination region set in the image region formed by B-mode data for one frame in the ultrasonic diagnostic apparatus according to the second embodiment. 
         FIG. 18  is a diagram for explaining a method of determining a structure and a parenchyma based on B-mode data for one frame in the ultrasonic diagnostic apparatus according to the second embodiment. 
         FIG. 19  is a diagram showing an example of a deep determination region set in the image region formed by B-mode data for one frame in the ultrasonic diagnostic apparatus according to the second embodiment. 
       Each of  FIGS. 20A and 20B  is a diagram showing an ultrasonic image when the transmission frequency is controlled. 
         FIG. 21  is a schematic diagram showing a configuration of an ultrasonic diagnostic apparatus according to a third embodiment. 
         FIG. 22  is a block diagram showing a configuration of a transmitting/receiving circuit in the ultrasonic diagnostic apparatus according to the third embodiment. 
         FIG. 23  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the third embodiment as a flowchart. 
         FIG. 24  is a diagram showing an operation of the ultrasonic diagnostic apparatus according to the third embodiment as a flowchart. 
       Each of  FIGS. 25A and 25B  is a diagram showing an ultrasonic image when the transmission frequency and the complex reception filter are controlled. 
     
    
    
     DETAILED DESCRIPTION 
     An ultrasonic diagnostic apparatus according to a present embodiment will be described with reference to the accompanying drawings. 
     The ultrasonic diagnostic apparatus according to the present embodiment includes an evaluating circuit, a frequency setting circuit, and a drive circuit. The evaluating circuit is configured to analyze a received signal of a predetermined depth based on received signals of ultrasonic wave to evaluate a degree of beam penetration to a deep portion. The frequency setting circuit is configured to set a transmission frequency based on a result evaluated by the evaluating circuit. The drive circuit is configured to generate a drive pulse based on the set transmission frequency. 
     1. Ultrasonic Diagnostic Apparatus according to First embodiment. 
       FIG. 1  is a schematic diagram showing a configuration of an ultrasonic diagnostic apparatus according to a first embodiment. 
       FIG. 1  shows an ultrasonic diagnostic apparatus  10  according to a first embodiment.  FIG. 1  shows an ultrasonic probe  20 , an input interface  30 , and a display  40 . Note that an apparatus in which at least one of the ultrasonic probe  20 , the input interface  30  and the display  40  are added to the ultrasonic diagnostic apparatus  10  may be referred to as “ultrasonic diagnostic apparatus”. In the following description, a case will be described in which the ultrasonic probe  20 , the input interface  30  and the display  40  are all provided outside the ultrasonic diagnostic apparatus  10 . 
     The ultrasonic diagnostic apparatus  10  includes a transmitting/receiving (T/R) circuit  11 , a B-mode processing circuit  12 , a Doppler processing circuit  13 , an image generating circuit  14 , an image memory  15 , a network interface  16 , processing circuitry  17 , and a main memory  18 . The circuits  11  to  14  are configured by application-specific integrated circuits (ASICs) and the like. However, the present invention is not limited to this case, and all or part of the functions of the circuits  11  to  14  may be realized by the processing circuitry  17  executing a program. 
     The T/R circuit  11  has a transmitting circuit T and a receiving circuit  112  (shown in  FIG. 4 ). Under the control of the processing circuitry  17 , the T/R circuit  11  controls transmission directivity and reception directivity in transmission and reception of ultrasonic waves. The case where the T/R circuit  11  is provided in the ultrasonic diagnostic apparatus  10  will be described, but the T/R circuit  11  may be provided in the ultrasonic probe  20 , or may be provided in both of the ultrasonic diagnostic apparatus  10  and the ultrasonic probe  20 . The T/R circuit  11  is one example of a transmitter-and-receiver. 
     The transmitting circuit T supplies a drive signal to the ultrasonic transducer of the ultrasonic probe  20 . The configuration of the transmitting circuit T will be described later with reference to  FIG. 4 . The receiving circuit  112  receives the received signal received by the ultrasonic transducers and performs various processing on the received signal to generate echo data. The configuration of the receiving circuit  112  will be described later with reference to  FIG. 4 . 
     The B-mode processing circuit  12  may change the frequency band to be visualized by changing the detection frequency using filtering processing. By using the filtering processing function of the B-mode processing circuit  12 , harmonic imaging such as the contrast harmonic imaging (CHI) or the tissue harmonic imaging (THI) is performed. 
     That is, the B-mode processing circuit  12  may separate the reflected waves from within a subject into which the contrast agent is injected into harmonic data (or sub-frequency data) and fundamental wave data. The harmonic data (or sub-frequency data) corresponds to reflected waves with a harmonic component whose reflection source is the contrast agent (microbubbles or bubbles) in the subject. The fundamental wave data corresponds to reflected waves with a fundamental wave component whose reflection source is tissue in the subject. The B-mode processing circuit  12  generates B-mode data for generating contrast image data based on the reflected wave data (reception signals) of the harmonic component, and generates B-mode data for generating fundamental wave image data based on the reflected wave data (reception signals) with the fundamental wave component. 
     In the THI by using the filtering processing function of the B-mode processing circuit  12 , it is possible to separate harmonic data or sub-frequency data which is reflected wave data (reception signals) of a harmonic component from reflected wave data of the subject. Then, the B-mode processing circuit  12  generates B-mode data for generating tissue image data in which the noise component is removed from the reflected wave data (reception signals) of the harmonic component. 
     When the CHI or THI harmonic imaging is performed, the B-mode processing circuit  12  may extract the harmonic component by a method different from the method using the above-described filtering. With respect to harmonic imaging, an imaging method called the amplitude modulation (AM) method, the phase modulation (PM) method or the AM-PM method in which the AM method and the PM method are combined is performed. With the AM method, the PM method, and the AM-PM method, ultrasonic transmission with different amplitudes and phases is performed multiple times on the same scanning line. 
     Thereby, the T/R circuit  11  generates and outputs multiple reflected wave data (reception signals) in each scanning line. The B-mode processing circuit  12  extracts harmonic components by performing addition/subtraction processing according to the modulation method on the multiple reflected wave data (reception signals) of each scanning line. The B-mode processing circuit  12  performs envelope detection processing etc. on the reflected wave data (reception signals) of the harmonic component to generate B-mode data. 
     For example, when the PM method is performed, the T/R circuit  11  controls the ultrasonic waves having the same amplitude and reversed-phase polarities, for example (−1, 1), to be transmitted twice by each scanning line under a scan sequence set by the processing circuitry  17 . The T/R circuit  11  generates a reception signal based on transmission of “−1” and a reception signal based on transmission of “1”. The B-mode processing circuit  12  adds these two reception signals. As a result, the fundamental wave component is removed, and a signal in which the second harmonic component mainly remains is generated. Then, the B-mode processing circuit  12  performs envelope detection processing and the like on such a signal to generate B-mode data using THI or CHI. 
     Alternatively, for example, in the THI, an imaging method using the second harmonic component and a difference tone component included in the reception signals has been put to practical use. With the imaging method using the difference tone component, transmission ultrasonic waves are transmitted from the ultrasonic probe  20 , and the transmission ultrasonic waves have, for example, a composite waveform in which a first fundamental waves with a center frequency “f 1 ” and a second fundamental waves with a center frequency “f 2 ” larger than the center frequency “f 1 ” are combined. Such a composite waveform is a waveform in which a waveform with the first fundamental waves and a waveform with the second fundamental waves which phases being adjusted with each other are combined, such that the difference tone component having the same polarity as the second harmonic component is generated. The T/R circuit  11  transmits the transmission ultrasonic waves of the composite waveform, for example, twice while inverting the phase. In such a case, for example, the B-mode processing circuit  12  removes the fundamental wave component by adding two reception signals, and performs an envelope detection process etc. after extracting a harmonic component in which the difference tone component and the second harmonic component are mainly left. 
     Under the control of the processing circuitry  17 , the Doppler processing circuit  13  frequency-analyzes the phase information from the echo data from the receiving circuit  112 , thereby generating data (2D or 2D data) acquired by extracting moving data of moving subject such as average speed, variance, power and the like for multiple points. This data is an example of the raw data, and is generally called “Doppler data”. In the present embodiment, the moving subject is, for example, blood flow, tissue such as heart wall, or contrast agent. The Doppler processing circuit  13  is one example of a Doppler processer. 
     Under the control of the processing circuitry  17 , the image generating circuit  14  generates an ultrasonic image presented in a predetermined luminance range as image data based on the reception signals received by the ultrasonic probe  20 . For example, the image generating circuit  14  generates, as an ultrasonic image, a B-mode image in which the intensity of the reflected wave is represented by luminance from the two-dimensional B-mode data generated by the B-mode processing circuit  12 . In addition, the image generating circuit  14  generates a color Doppler image from the two-dimensional Doppler data generated by the Doppler processing circuit  13 . The color Doppler image includes an average speed image representing moving state information, a variance image, a power image, or a combination image thereof. The image generating circuit  14  is an example of an image generating unit. 
     In the present embodiment, the image generating circuit  14  generally converts (scan-converts) a scanning line signal sequence of ultrasonic scanning into a scanning line signal sequence of a video format used by a television or the like, and generates ultrasonic image data for display. Specifically, the image generating circuit  14  generates ultrasonic image data for display by performing coordinate conversion according to the ultrasonic scanning mode of the ultrasonic probe  20 . The image generating circuit  14  performs various image processes other than the scan conversion. For example, the image generating circuit  14  performs image processing (smoothing processing) for regenerating an average luminance image using multiple image frames after scan conversion, image processing using a differential filter in the image (processing for enhancing edges) and the like. Further, the image generating circuit  14  combines character information of various parameters, scales, body marks, and the like with the ultrasonic image data. 
     That is, the B-mode data and the Doppler data are the ultrasonic image data before the scan conversion processing. The data generated by the image generating circuit  14  is ultrasonic image data for display after the scan conversion processing. The B-mode data and the Doppler data are also called raw data. The image generating circuit  14  generates two-dimensional ultrasonic image data for display from the two-dimensional ultrasonic image data before the scan conversion processing. 
     Further, the image generating circuit  14  performs coordinate conversion on the three-dimensional B-mode data generated by the B-mode processing circuit  12 , thereby generates three-dimensional B-mode image data. The image generating circuit  14  performs coordinate conversion on the three-dimensional Doppler data generated by the Doppler processing circuit  13 , thereby generates three-dimensional Doppler image data. The image generating circuit  14  generates “three-dimensional B-mode image data or three-dimensional Doppler image data” as “three-dimensional ultrasonic image data (volume data)”. 
     Further, the image generating circuit  14  performs a rendering processing on the volume data to generate various two-dimensional image data for displaying the volume data on the display  40 . The image generating circuit  14  performs a processing of generating a multi planer reconstruction (MPR) image data from the volume data by performing, for example, an MPR processing that is one of the rendering processing. Further, the image generating circuit  14  performs, for example, volume rendering (VR) processing for generating two-dimensional image data reflecting three-dimensional data that is one of the rendering processing. 
     The image memory  15  includes multiple memory cells in one frame in two axial directions, and includes a two-dimensional memory which is a memory provided with multiple frames. The two-dimensional memory as the image memory  15  stores one frame or an ultrasonic image of the multiple frames generated by the image generating circuit  14  as two-dimensional image data under the control of the processing circuitry  17 . The image memory  15  is an example of a storage. 
     Under the control of the processing circuitry  17 , the image generating circuit  14 , if necessary, performs three-dimensional reconstruction for performing an interpolation processing on the ultrasonic images arranged in the two-dimensional memory as the image memory  15 , thereby generates an ultrasonic image as volume data in the three-dimensional memory as the image memory  15 . A known technique is used as the interpolation processing. 
     The image memory  15  may include a three-dimensional memory which is a memory having multiple memory cells in three axis directions (X-axis, Y-axis, and Z-axis directions). 
     The three-dimensional memory as the image memory  15  stores the ultrasonic image generated by the image generating circuit  14  as volume data under the control of the processing circuitry  17 . 
     The network interface  16  implements various information communication protocols according to the network form. The network interface  16  connects the ultrasonic diagnostic apparatus  10  and other devices such as the external medical image managing apparatus  60  and the medical image processing apparatus  70  according to these various protocols. An electrical connection or the like via an electronic network is applied to this connection. In the present embodiment, the electronic network means an entire information communication network using telecommunications technology. The electronic network includes a wired/wireless hospital backbone local area network (LAN) and the Internet network, as well as a telephone communication line network, an optical fiber communication network, a cable communication network, a satellite communication network, or the like. 
     Further, the network interface  16  may implement various protocols for non-contact wireless communication. In this case, the ultrasonic diagnostic apparatus  10  can directly transmit/receive data to/from the ultrasonic probe  20 , for example, without going through the network. The network interface  16  is one example of a network connector. 
     The processing circuitry  17  may mean a processor such as a dedicated or general-purpose CPU (central processing unit), an MPU (microprocessor unit), a GPU (Graphics Processing Unit), or the like. The processing circuitry  17  may mean an ASIC, a programmable logic device, or the like. The programmable logic device is, for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA). 
     Further, the processing circuitry  17  may be constituted by a single circuit or a combination of independent circuit elements. In the latter case, the main memory  18  may be provided individually for each circuit element, or a single main memory  18  may store programs corresponding to the functions of the circuit elements. The processing circuitry  17  is one example of a processor. 
     The main memory  18  is constituted by a semiconductor memory element such as a random-access memory (RAM), a flash memory, a hard disk, an optical disk, or the like. The main memory  18  may be constituted by a portable medium such as a universal serial bus (USB) memory and a digital video disk (DVD). The main memory  18  stores various processing programs (including an operating system (OS) and the like besides the application program) used in the processing circuitry  17  and data necessary for executing the programs. In addition, the OS may include a graphical user interface (GUI) which allows the operator to frequently use graphics to display information on the display  40  to the operator and can perform basic operations by the input interface  30 . The main memory  18  is one example of a storage. 
     The ultrasonic probe  20  includes microscopic transducers (piezoelectric elements) on the front surface portion, and transmits and receives ultrasonic waves to a region including a scan target, for example, a region including a lumen. Each transducer is an electroacoustic transducer, and has a function of converting electric pulses into ultrasonic pulses at the time of transmission and converting reflected waves to electric signals (reception signals) at the time of reception. The ultrasonic probe  20  is configured to be small and lightweight, and is connected to the ultrasonic diagnostic apparatus  10  via a cable (or wireless communication). 
     The ultrasonic probe  20  is classified into types such as a linear type, a convex type, a sector type, etc. depending on differences in scanning system. Further, the ultrasonic probe  20  is classified into a 1D array probe in which transducers are arrayed in a one-dimensional (1D) manner in the azimuth direction, and a 2D array probe in which transducers are arrayed in a two-dimensional (2D) manner in the azimuth direction and in the elevation direction, depending on the array arrangement dimension. The 1D array probe includes a probe in which a small number of transducers are arranged in the elevation direction. 
     In the present embodiment, when a three-dimensional (3D) scan, that is, a volume scan is executed, the 2D array probe having a scan type such as the linear type, the convex type, the sector type, or the like is used as the ultrasonic probe  20 . Alternatively, when the volume scan is executed, the 1D probe having a scan type such as the linear type, the convex type, the sector type and the like and having a mechanism that mechanically oscillates in the elevation direction is used as the ultrasonic probe  20 . The latter probe is also called a mechanical 4D probe. 
     The input interface  30  includes an input device operable by an operator, and a circuit for inputting a signal from the input device. The input device may be a trackball, a switch, a mouse, a keyboard, a touch pad for performing an input operation by touching an operation surface, a touch screen in which a display screen and a touch pad are integrated, a non-contact input circuit using an optical sensor, an audio input circuit, and the like. When the input device is operated by the operator, the input interface  30  generates an input signal corresponding to the operation and outputs it to the processing circuitry  17 . 
     The input interface  30  may further include an adjustment switch for adjusting a frequency characteristic of a reception filter to be described later. The input interface  30  is one example of an input unit. 
     The display  40  is constituted by a general display output device such as a liquid crystal display or an organic light emitting diode (OLED) display. The display  40  displays various kinds of information under the control of the processing circuitry  17 . The display  40  is one example of a display unit. 
       FIG. 1  shows the medical image managing apparatus  60  and the medical image processing apparatus  70  which are external devices of the ultrasonic diagnostic apparatus  10 . The medical image managing apparatus  60  is, for example, a digital imaging and communications in medicine (DICOM) server, and is connected to a device such as the ultrasonic diagnostic apparatus  10  such that data can be transmitted and received via the network N. The medical image managing apparatus  60  manages a medical image such as an ultrasonic image generated by the ultrasonic diagnostic apparatus  10  as the DICOM file. 
     The medical image processing apparatus  70  is connected to devices such as the ultrasonic diagnostic apparatus  10  and the medical image managing apparatus  60  such that data is transmitted and received via the network N. An Example of the medical image processing apparatus  70  includes a workstation that performs various image processing on the ultrasonic image generated by the ultrasonic diagnostic apparatus  10  and a portable information processing terminal such as a tablet terminal. It should be noted that the medical image processing apparatus  70  is an offline apparatus and may be an apparatus capable of reading an ultrasonic image generated by the ultrasonic diagnostic apparatus  10  via a portable storage medium. 
     Subsequently, the concept of the configuration and function of the receiving circuit  112  provided in the T/R circuit  11  will be described with reference to  FIGS. 2 and 3 . 
     The receiving circuit  112  provided in the T/R circuit  11  has a frequency characteristic analysis circuit (for example, “frequency characteristic analysis circuit  57 ” shown in  FIG. 4 ), a filter setting circuit (for example, “filter setting circuit  58 ” shown in  FIG. 4 ), and a filter processing circuit (for example, “filter processing circuit  56 ” shown in  FIG. 4 ). The frequency characteristic analysis circuit perform a frequency analysis on a reception signal of a predetermined depth based on the reception signals of the ultrasonic wave from the ultrasonic probe  20 , and acquires the frequency characteristic. The filter setting circuit sets a reception filter that corrects the frequency characteristic at a predetermined depth such that the frequency characteristic at a predetermined depth acquired by the frequency characteristic analysis circuit shows the predetermined frequency characteristic. The filter processing circuit applies the reception filter set by the filter setting circuit to the reception signal of a predetermined depth such that feedback is performed. For example, the frequency characteristic analysis circuit perform the frequency-analysis on a reception signal in each region of interest according to the depth and acquires a frequency characteristic in each region of interest. The filter setting circuit sets a reception filter that corrects the frequency characteristic of each region of interest in each region of interest such that the frequency characteristic of each region of interest acquired by the frequency characteristic analysis circuit shows a predetermined frequency characteristic. The filter processing circuit applies the reception filter in each region of interest set by the filter setting circuit to the reception signal in each region of interest such that feedback is performed. 
     That is, the filter setting circuit sets a reception filter that is variable according to the depth and that corrects the reception signal so as to exhibit a frequency characteristic having a substantially flat bandwidth over a wide range. It should be noted that “substantially flat” means that the absolute value of the slope of the tangent line formed by each point on the waveform is equal to or smaller than a threshold value, that is, it is rather level. In addition, the reception filter may correct the reception signal so as to exhibit symmetrical (for example, Gaussian function) frequency characteristic on the low frequency side and the high frequency side with respect to the center frequency. 
       FIG. 2  is a conceptual diagram for explaining a target frequency characteristic having the substantially flat bandwidth close to a designed frequency characteristic. 
     The left side of each of  FIGS. 2A and 2B  shows a designed frequency characteristic. The center of each of  FIGS. 2A and 2B  shows a frequency characteristic based on a reception signal in the region of interest in the clinic practice. The right side of each of  FIGS. 2A and 2B  shows a target frequency characteristic having a frequency characteristic of a substantially flat bandwidth close to a substantially flat bandwidth in design.  FIG. 2A  shows a frequency characteristic particularly in a shallow part when ultrasonic attenuation is small and high frequency is dominant in the clinical practice.  FIG. 2B  shows a frequency characteristic particularly in a deep part when ultrasonic attenuation is large and low frequency is dominant in clinical practice. 
     The filter setting circuit calculates a target frequency characteristic shown on the right side based on a designed frequency characteristic shown on the left side of  FIG. 2A  and a clinical frequency characteristic shown at the center. For example, the target frequency characteristic has a characteristic that becomes substantially flat in a wide band. 
     As shown on the right side of  FIG. 2A , the target frequency characteristic has a wide band on the high frequency side, and the intensity is not biased between the high frequency side and the low frequency side. The reception filter set by the filter setting circuit shapes the waveform of the clinical frequency characteristic such that the clinical frequency characteristic shown at the center of  FIG. 2A  is close to a substantially flat bandwidth shown on the left side. 
     On the other hand, the filter setting circuit calculates a target frequency characteristic shown on the right side based on a designed frequency characteristic shown on the left side of  FIG. 2B  and a clinical frequency characteristic shown at the center. For example, the target frequency characteristic has a characteristic that becomes substantially flat in a wide band. 
     As shown on the right side of  FIG. 2B , the target frequency characteristic has a wide band on the low frequency side, and the intensity is not biased between the high frequency side and the low frequency side. The reception filter set by the filter setting circuit shapes the waveform of the clinical frequency characteristic such that the clinical frequency characteristic shown at the center of FIG.  2 B is close to a substantially flat bandwidth shown on the left side. 
     Each of  FIGS. 3A to 3E  is a conceptual diagram for explaining a method of setting a reception filter. 
       FIG. 3A  shows frequency characteristic acquired by frequency-analyzing a reception signal in a region of interest corresponding to the depth among reception signals of one frame.  FIG. 3A  has the same waveform as shown at the center of  FIG. 2B .  FIG. 3B  shows the gravity center calculated based on the frequency characteristic shown in  FIG. 3A  in a broken line.  FIG. 3C  shows a target signal strength calculated from the frequency characteristic shown in  FIG. 3A . 
       FIG. 3D  shows, in a thick solid line, a frequency characteristic having the signal strength shown in  FIG. 3C  and having a substantially flat bandwidth close to the target substantially flat bandwidth.  FIG. 3E  shows, in a thick solid line, in which the frequency characteristic of  FIG. 3A  is set to indicate the target frequency characteristic of  FIG. 3D . 
     As shown in  FIGS. 3A to 3E , the filter setting circuit sets a reception filter, thereby brings the substantially flat bandwidth indicated by the frequency characteristic of the reception signal in each region of interest in the clinical practice closer to the substantially flat bandwidth indicated by the designed frequency characteristic. 
     The reception signals for acquiring the frequency characteristic may be RF signals or I/Q signals. That is, the beamforming method may be RF beamforming or I/Q beamforming. With the RF beamforming method, the RF signals are delayed and added, subjected to quadrature detection (demodulation), converted into I/Q signals each including an “I (In-phase)” signal and a “Q (Quadrature-phase)” signal, and an ultrasonic image is generated. With the I/Q beamforming method, the RF signals are subjected to quadrature detection, converted to an I/Q basebands, delayed and added, and an ultrasonic image is generated. Hereinafter, a case where the reception signals for acquiring frequency characteristic are the I/Q signals, that is, a case where the I/Q beamforming is adopted, will be described as an example unless otherwise specified. 
     Subsequently, a specific configuration and functions of the receiving circuit  112  provided in the T/R circuit  11  will be described with reference to  FIGS. 4 to 12 . 
       FIG. 4  is a block diagram showing the configuration of the T/R circuit  11 . 
       FIG. 4  shows a transmitting circuit T provided in the T/R circuit  11  and a receiving circuit  112 . The transmitting circuit T has a pulse generating circuit T 1 , a transmission delay circuit T 2 , a drive circuit (e.g., pulsar), and supplies a drive signal to ultrasonic transducers. The pulse generating circuit T 1  repeatedly generates rate pulses for forming transmission ultrasonic waves at a predetermined rate frequency. The transmission delay circuit T 2  converges the ultrasonic waves generated from the ultrasonic transducer of the ultrasonic probe  20  into a beam shape, and gives a delay time of each piezoelectric transducer necessary for determining the transmission directivity to each rate pulse generated by the pulse generating circuit T 1 . The transmission delay circuit T 2  arbitrarily adjusts the transmission direction of the ultrasonic beam transmitted from a piezoelectric transducer surface by changing the delay time given to each rate pulse. The drive circuit T 3  applies a drive pulse to the ultrasonic transducer at a timing based on the rate pulse. 
     The receiving circuit  112  includes an amplifier  51 , an analog to digital (A/D) conversion circuit  52 , a quadrature detection circuit  53 , a reception delay circuit  54 , an addition circuit  55 , a filter processing circuit  56 , a frequency characteristic analysis circuit  57 , and a filter setting circuit  58 . 
     The amplifier  51  has a function of amplifying signals received from the ultrasonic probe  20  for each channel and performing a gain correction processing under the control of the processing circuitry  17 . The amplifier  51  can improve the image quality of the ultrasonic image by controlling the gain. 
     The A/D conversion circuit  52  has a function of subjecting the gain-corrected reception signals, which is the output of the amplifier  51 , to A/D conversion for each channel under the control of the processing circuitry  17 . 
     The quadrature detection circuit  53  has a function of performing quadrature detection on RF signals that are reception signals and converting the RF signals into I/Q signals each including an “I” signal and a “Q” signal for each channel. 
     The reception delay circuit  54  has a function of giving, for each channel, a delay time necessary for determining the reception directivity to the I/Q signals output from the quadrature detection circuit  53  under the control of the processing circuitry  17 . The reception delay circuit  54  can improve the image quality of the ultrasonic image by controlling the reception delay curve given to the I/Q signals. 
     The addition circuit  55  has a function of performing phase rotation and weighting control (apodization) for each channel on the I/Q signals output from the reception delay circuit  54  to acquire the I/Q signals, thereby adding the acquired I/Q signals and generating beam data of the I/Q signals. By the addition processing of the addition circuit  55 , a reflection component from a direction corresponding to the reception directivity of the reception signals is emphasized. 
     The filter processing circuit  56  has a function of applying an arbitrary complex reception filter to the I/Q signals output from the addition circuit  55  under the control of the processing circuitry  17 , and a function of outputting the I/Q signals to which the complex reception filter has been applied to the B-mode processing circuit  12  and the Doppler processing circuit  13 . The filter processing circuit  56  is an example of a filter processor. 
     As described above, the image quality of the ultrasonic image can be improved to some extent by the gain control by the amplifier  51  and the control of the reception delay curve by the reception delay circuit  54 . However, since the ultrasonic attenuation changes for each individual and of each depth, it is difficult to optimize the image quality of the ultrasonic wave only by controlling those. Therefore, the receiving circuit  112  provided in the T/R circuit  11  includes the frequency characteristic analysis circuit  57  and the filter setting circuit  58 . 
     The frequency characteristic analysis circuit  57  has a function of performing a frequency analysis on an I/Q signal in each region of interest according to the depth under the control of the processing circuitry  17  based on the I/Q signals output from the addition circuit  55 , thereby acquiring a frequency characteristic. For example, the frequency characteristic analysis circuit  57  can perform frequency analysis by performing a fast Fourier transform (FFT) on the I/Q signal in each region of interest. The frequency characteristic analysis circuit  57  is one example of a frequency characteristic analyzer. 
     The filter setting circuit  58  sets, under the control of the processing circuitry  17 , a complex reception filter in each region of interest, which is output from the frequency characteristic analysis circuit  57 , such that the frequency characteristic of each region of interest shows a predetermined frequency characteristic. The filter coefficient of the complex reception filter is a complex coefficient including a real part and an imaginary part. In the case of the I/Q beamforming, when the waveform of the I/Q signal in each region of interest slightly changes the frequency of the waveform of the RF signal, the modulated signal can be treated as a complex amplitude. The filter setting circuit  58  is one example of a filter setting unit. Under the control of the processing circuitry  17 , the filter processing circuit  56  includes a function of applying the complex reception filter of each region of interest output from the filter setting circuit  58  to the I/Q signals output from the addition circuit  55  such that feedback is performed, and a function of outputting the I/Q signals to which the complex reception filter has been applied to the B-mode processing circuit  12  or the Doppler processing circuit  13  as baseband data, in addition to the function described above. 
     sequently, an operation of the ultrasonic diagnostic apparatus  10  will be described. 
     Each of  FIGS. 5 and 6  is a diagram showing the operation of the ultrasonic diagnostic apparatus  10  as a flowchart. In  FIGS. 5 and 6 , reference numerals with numbers attached to “ST” indicate respective steps in the flowchart. In  FIGS. 5 and 6 , the case of I/Q beamforming, that is, the case where the reception filter is a complex reception filter will be described as an example. 
     As shown in  FIG. 5 , the processing circuitry  17  of the ultrasonic diagnostic apparatus  10  controls the T/R circuit  11  and the like to start an ultrasonic scan using the ultrasonic probe  20  (step ST 1 ). 
     The frequency characteristic analysis circuit  57  acquires I/Q signals for one frame, which are the output of the addition circuit  55  (step ST 2 ). The frequency characteristic analysis circuit  57  performs the frequency analysis on an I/Q signal in the region of interest corresponding to the depth among the I/Q signals for one frame acquired in step ST 2  to acquire frequency characteristic (step ST 3 ). 
     filter setting circuit  58  sets a complex reception filter for correcting the waveform of the frequency characteristic of the region of interest such that the frequency characteristic of the region of interest acquired in step ST 3  shows a predetermined frequency characteristic specifically, it is based on steps ST 4  to ST 8  described later. 
     The filter setting circuit  58  calculates the gravity center from the frequency characteristic of the region of interest acquired in step ST 3  (step ST 4 ). 
     The filter setting circuit  58  sets a target signal strength (step ST 5 ). The filter setting circuit  58  sets a target frequency characteristic, based on the waveform of the frequency characteristic acquired in step ST 3 , the gravity center set in step ST 4 , the target signal strength set in step ST 5 , and the substantially flat bandwidth indicated by the designed frequency characteristic (step ST 6 . The designed frequency characteristic is set in advance before the ultrasonic scan is started, or is optimized according to the acquired frequency characteristic. 
     For example, the filter setting circuit  58  acquires a reception filter coefficient having a target signal strength near the position of the gravity center and having a substantially flat bandwidth close to a substantially flat bandwidth in design. The receive filter coefficient is based on a waveform of clinical frequency characteristic acquired in step ST 3 . 
     The filter setting circuit  58  sets a complex reception filter for the region of interest, and the complex reception filter shapes the waveform such that the frequency characteristic of the I/Q signal in the region of interest acquired in step ST 3  indicates the target frequency characteristic set in step ST 6  (step ST 7 ), and stores the complex reception filter of the region of interest in the main memory  18  (step ST 8  ). The operator may adjust the frequency characteristic of the set complex reception filter via the input interface  30  (adjustment switch). 
     Each of  FIGS. 7A and 7B  is a diagram showing a complex reception filter of the region of interest. 
       FIG. 7A  shows a frequency characteristic of an I/Q signal in the region of interest, a target frequency characteristic of the region of interest, and a frequency characteristic of a complex reception filter of the region of interest. A complex reception filter for shaping the waveform is set for each region of interest such that the frequency characteristic of the I/Q signal in the region of interest indicates the target frequency characteristic. 
     In the case of I/Q beamforming, when the waveform of the I/Q signal in each region of interest slightly changes the frequency of the waveform of the RF signal, the modulated signal can be treated as a complex amplitude. The filter coefficient of the complex reception filter is a complex coefficient including a real part and an imaginary part. 
     Returning to the description of  FIG. 5 , the filter setting circuit  58  determines whether or not complex reception filters have been set at all depths, that is, in all regions of interest (step ST 9 ). If it is determined as “NO” in step ST 9 , that is, if it is determined that the complex reception filters are not set in all the regions of interest, the frequency characteristic analysis circuit  57  shifts the depth of the region of interest (step ST 10 ), and frequency-analyzes the shifted I/Q signal in the region of interest based on the I/Q signal for one frame acquired in step ST 2  to acquire frequency characteristic (step ST 3 ). 
     On the other hand, if it is determined as “YES” in step ST 9 , that is, if it is determined that the complex reception filters have been set in all the regions of interest, the processing proceeds to the steps in  FIG. 6 . 
     Each of  FIGS. 8A and 8B  is a diagram showing a complex reception filter of each region of interest.  FIG. 8  shows a complex reception filter of each region of interest when divided into eight in the depth direction. 
       FIG. 8A  shows the filter coefficients of the real part components in each region of interest, that is, at each depth.  FIG. 8B  shows the filter coefficient of the imaginary part component in each region of interest, that is, at each depth. As shown in  FIGS. 8A and 8B , appropriate filter coefficients are calculated for the real part component and the imaginary part component of each region of interest. 
     Returning to the description of  FIG. 6 , the filter processing circuit  56  applies the complex reception filter in each region of interest registered in step ST 8  to the I/Q signals of one frame output from the addition circuit  55  such that feedback is performed (step ST 11 ). 
       FIG. 9  is a diagram showing, as a frequency characteristic, an effect acquired when a complex reception filter is applied to the I/Q signal in a predetermined region of interest. 
       FIG. 9  shows frequency characteristic before a complex reception filter is applied to I/Q signals for one frame.  FIG. 9  also shows frequency characteristic after applying a complex reception filter to I/Q signal in a predetermined region of interest among I/Q signals for one frame. The complex reception filter in each region of interest registered in step ST 8  is fed back and applied to the I/Q signals for one clinical frame, which is the output of the addition circuit  55 . As a result, the frequency characteristic of the I/Q signals for one clinical frame are corrected to the target frequency characteristic, and a substantially flat bandwidth is expanded. 
     Returning to the description of  FIG. 6 , the B-mode processing circuit  12  (or Doppler processing circuit  13 ) and the image generating circuit  14  generate an ultrasonic image for one frame based on the I/Q signals in the entire range to which the complex reception filter has been applied in step ST 11  (step ST 12 ). 
     Each of  FIGS. 10A and 10B  is a diagram showing an effect acquired when a complex reception filter is applied to the I/Q signal in a predetermined region of interest as an ultrasonic image (for example, a B-mode image). The imaging target (part) of the B-mode image shown in each of  FIGS. 10A and 10B  is a kidney. 
       FIG. 10A  shows a B-mode image before applying a complex reception filter to I/Q signals for one frame.  FIG. 10B  shows a B-mode image after applying a complex reception filter to an I/Q signal in a predetermined region of interest, for example, a region of interest R, of I/Q signals for one frame. 
     The B-mode image region shown in  FIG. 10A  is compared with the B-mode image region shown in  FIG. 10B . According to the B-mode image region shown in  FIG. 10B , the distance resolution of the structure in the region of interest R of the kidney is improved. As a result, the image quality is optimized, and it is possible to more clearly recognize the area of interest R. 
     Returning to the description of  FIG. 6 , the processing circuitry  17  determines whether to finish the ultrasonic scan started in step ST 1  (step ST 13 ). For example, the processing circuitry  17  determines whether or not to finish the ultrasonic scan by a finish operation by the operator via the input interface  30 . If it is determined as “NO” in step ST 13 , that is, if it is determined that the ultrasonic scan started in step ST 1  is not to be finished, proceed to the next frame (step ST 14 ), and the filter processing circuit  56  applies the coefficients of the complex reception filter registered in step ST 8  to the I/Q signals of the next one frame such that feedback is performed (step ST 11 ). 
     On the other hand, if it is determined as “YES” in step 
     ST 13 , that is, if it is determined that the ultrasonic scan started in step ST 1  is to be finished, the processing circuit  17  of the ultrasonic diagnostic apparatus  10  controls the T/R circuit  11  and the like, thereby finishes the ultrasonic scan using the ultrasonic probe  20 . 
     The case where, in the ultrasonic scan for the same patient and the same imaging part, the complex reception filter set and registered once is applied to I/Q signals of frames generated thereafter has been described with reference to  FIGS. 5 and 6 . In other words, the same complex reception filter is used during a series of ultrasonic examinations for scanning the same imaging part. However, it is not limited to that case. For example, the complex reception filter may be set every time in each frame, or may be set at fixed intervals. The necessity of setting the complex reception filter may be switched of each frame according to the movement of the ultrasonic probe  20 . 
     In this case, the frequency characteristic analysis circuit  57  determines whether or not the change in the value indicating the scan cross-section is equal to or greater than the threshold value. Then, the frequency characteristic analysis circuit  57  may perform frequency analysis of the I/Q signal again, or may return to the complex reception filter originally set in the apparatus as a fixed value when the change in the value indicating the scan cross-section is equal to or greater than the threshold value and when there is almost no change in the value indicating the scan cross-section, that is, the change less than the threshold value. The value indicating the scan cross-section is a value indicating at least one of the positions and angles of the ultrasonic probe  20  corresponding to the scan cross-section. 
     Alternatively, the value indicating the scan cross-section is the luminance value of the ultrasonic image corresponding to the scan cross-section. The luminance value of the ultrasonic image refers to a variation in the average luminance value, the maximum luminance value, the minimum luminance value, or the luminance value in pixels constituting the ultrasonic image (or a region of interest thereof). 
     That is, the complex reception filter is not reset while the position and angle of the ultrasonic probe  20  change to some extent between frames. This is because the change in the value indicating the scan cross-section exceeds the threshold value. Alternatively, the complex reception filter is not reset while the average luminance values of the pixels constituting the ultrasonic image (or the region of interest thereof) change to some extent between frames. This is because the change in the value indicating the scan cross-section exceeds the threshold value. The change in the value indicating the scan cross-section may be based on data acquired by an acceleration sensor (not shown) or a magnetic sensor (not shown). The acceleration sensor can measure the angle of the ultrasonic probe  20  provided in the ultrasonic probe  20 . The magnetic sensor can generate a magnetic field to measure the position and angle of the ultrasonic probe  20 . Alternatively, when the sensor is not used, a change in the value indicating the scan cross-section may be detected from the time change of the image information. 
     Further, the complex reception filter set in the past and the value indicating the scan cross-section (e.g., the position of the ultrasonic probe  20 ) may be registered in the main memory  18 . In this case, if it is determined that a scan cross-section of the same position has been scanned in a series of ultrasonic examinations in the past, the filter processing circuit  56  acquires and uses a complex reception filter corresponding to the scan cross-section from the main memory  18 . Thereby, the load for setting the complex reception filter is reduced. 
     Designed frequency characteristic is distorted due to the amount of ultrasonic attenuation from the designed frequency band. However, according to the ultrasonic diagnostic apparatus  10 , it is possible to correct instantaneously (or almost in real time) the distortion. As a result, it is possible to suppress image quality degradation due to ultrasonic attenuation, thereby provide a high-quality ultrasonic image. 
     2. First Modification 
     The filter setting circuit  58  is not limited to acquiring one target frequency characteristic from the frequency characteristic of the I/Q signal in each region of interest in order to set the reception filter. For example, the filter setting circuit  58  compounds multiple frequency components, that is, generates an ultrasonic image by frequency compounding. In this case, a complex reception filter is set for each frequency component set in each region of interest. The filter setting circuit  58  acquires a target frequency characteristic on the low frequency side and a target frequency characteristic on the high frequency side from the frequency characteristic of the I/Q signal in each region of interest. 
     In this case, the filter processing circuit  56  corrects the clinical frequency characteristic so as to show the frequency characteristic of each target. Then, the image generating circuit  14  synthesizes the ultrasonic images acquired with the frequency characteristic of each target. As a result, it is effective in improving the contrast resolution and improving the uniformity of the resulting image. 
       FIG. 11  is a diagram for explaining the frequency compound. 
     The upper part of  FIG. 11  shows the target, that is, the target frequency characteristic (center frequency f 1 ) on the low frequency side and the target frequency characteristic (center frequency f 2 ) on the high frequency side in the region of interest at the depth of the imaging target. The lower part of  FIG. 11  shows a target frequency characteristic on the low frequency side (center frequency f 1 ) and a target frequency characteristic on the high frequency side (center frequency f 2 ) in a deep region of interest where ultrasonic attenuation is large. When frequency compounding is performed, as shown in  FIG. 11 , it is preferable that the level, that is, the intensity is matched between the target frequency characteristic on the low frequency side and the target frequency characteristic on the high frequency side. 
     3. Second Modification 
     When performing the frequency analysis on the I/Q signal in each region of interest according to the depth, the frequency characteristic analysis circuit  57  may set each region of interest to include the center position in the scanning direction in the image region. This is because the desired area is often near the center of the image region. However, it is not limited to that case. For example, the frequency characteristic analysis circuit  57  can also set multiple regions of interest of the same depth and perform frequency analysis in a region of interest selected from the set multiple regions of interest. 
       FIG. 12  is a diagram showing a method of selecting a predetermined region of interest from the set multiple regions of interest of the same depth. 
       FIG. 12  simulates the image region of the B-mode image. Multiple regions of interest are set of the same depth along the scanning direction (the horizontal direction in  FIG. 12 ). Then, the frequency characteristic analysis circuit  57  performs noise determination on the multiple regions of interest of the same depth. The frequency characteristic analysis circuit  57  determines whether the signal to noise (SN) is higher than a threshold value for the multiple regions of interest of the same depth in order from the center position in the scanning direction to the outer position. For example, the frequency characteristic analysis circuit  57  performs noise determination in the region of interest at the center position in the scanning direction at the shallowest part of the image region. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is a signal region, and performs a frequency analysis in the region of interest. 
     Subsequently, the frequency characteristic analysis circuit  57  performs noise determination in the region of interest at the center position in the scanning direction in the second shallowest part of the image region. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is a noise region. Subsequently, in the second shallowest part of the image region, the frequency characteristic analysis circuit  57  performs a noise determination in the region of interest on the left of the center position. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is the signal region, and performs frequency analysis in the region of interest. 
     Subsequently, the frequency characteristic analysis circuit  57  performs a noise determination in the region of interest at the center position in the scanning direction in the third shallowest part of the image region. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is the noise region. 
     Subsequently, the frequency characteristic analysis circuit  57  performs noise determination in the region of interest on the left of the center position in the third shallowest part of the image region. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is the noise region. Subsequently, the frequency characteristic analysis circuit  57  performs noise determination in the region of interest on the right of the center position in the third shallowest part of the image region. Thereafter, the frequency characteristic analysis circuit  57  determines that the region of interest is the signal region, and performs frequency analysis in the region of interest. 
     In the present embodiment, none of the regions of interest at a certain depth may be the signal region. In this case, a dynamic filter preset in the apparatus may be used, one reception filter set at one shallower or deeper depth may be used, or a representative value (e.g., an average value) of two reception filters set at one shallower and deeper depth may be interpolated and used as the reception filter of the depth. 
     As described above, according to the ultrasonic diagnostic apparatus  10 , by controlling the complex reception filter according to the depth, deterioration of image quality due to ultrasonic attenuation can be suppressed. Thereby, it is possible to provide a high-quality ultrasonic image. 
     4. Ultrasonic Diagnostic Apparatus According to Second Embodiment 
     The first embodiment described above realizes the provision of the high-quality ultrasonic image by controlling the receiving side of the ultrasonic wave, that is, the complex receiving filter according to the depth. However, the provision of the high-quality ultrasonic image may be realized by controlling the transmission side of the ultrasonic wave, that is, the transmission frequency according to a degree of beam penetration to a deep portion. A case will be described below as an ultrasonic diagnostic apparatus according to the second embodiment. 
       FIG. 13  is a schematic view showing a configuration of the ultrasonic diagnostic apparatus according to a second embodiment. 
       FIG. 13  shows the ultrasonic diagnostic apparatus  10 A according to the second embodiment. Further,  FIG. 13  shows an ultrasonic probe  20 , an input interface  30 , and a display  40 . An apparatus in which at least one of an ultrasonic probe  20 , an input interface  30 , and a display  40  is added to the ultrasonic diagnostic apparatus  10 A may be referred to as an “ultrasonic diagnostic apparatus”. In the following description, a case where the ultrasonic probe  20 , the input interface  30 , and the display  40  that are all provided outside the ultrasonic diagnostic apparatus  10 A will be described. 
     The ultrasonic diagnostic apparatus  10 A includes a T/R circuit  11 A, a B-mode processing circuit  12 , a Doppler processing circuit  13 , an image generating circuit  14 , an image memory  15 , a network interface  16 , processing circuitry  17 , and a main memory  18 . The circuits  11 A,  12  to  14  are configured by an integrated circuit for a specific application or the like. However, the present invention is not limited to this case, and all or a part of the functions of the circuits  11 A,  12  to  14  may be realized by the processing circuitry  17  executing the program. 
     In  FIG. 13 , the same parts as those shown in  FIG. 1  are designated by the same reference numerals, and the description thereof will be omitted. 
     The T/R circuit  11 A includes a transmitting circuit  111  and a receiving circuit U (shown in  FIG. 14 ). The T/R circuit  11 A controls the transmission directivity and the reception directivity in the transmission/reception of ultrasonic waves under the control of the processing circuitry  17 . The case where the T/R circuit  11 A is provided in the ultrasonic diagnostic apparatus  10 A will be described, but the T/R circuit  11 A may be provided in the ultrasonic probe  20 , or may be provided in both the ultrasonic diagnostic apparatus  10 A and the ultrasonic probe  20 . The T/R circuit  11 A is one example of a transmitter-and-receiver. 
     The transmitting circuit  111  supplies a drive signal to the ultrasonic transducer of the ultrasonic probe  20 . The configuration of the transmitting circuit  111  will be described later with reference to  FIG. 14 . The receiving circuit U receives the received signal received by the ultrasonic transducer and performs various processing on the received signal to generate echo data. The configuration of the receiving circuit U will be described later with reference to  FIG. 14 . 
       FIG. 14  is a block diagram showing a configuration of the T/R circuit  11 A.  FIG. 14  shows a transmitting circuit  111  and a receiving circuit U provided in the T/R circuit  11 A. The receiving circuit U includes an amplifier U 1 , an A/D conversion circuit U 2 , a quadrature detection circuit U 3 , a reception delay circuit U 4 , an adder circuit U 5 , and a filter processing circuit U 6 . The receiving circuit U receives the echo signal received by the ultrasonic vibrator and performs various processing on the echo signal to generate echo data. 
     The amplifier U 1 , the A/D conversion circuit U 2 , the quadrature detection circuit U 3 , the reception delay circuit U 4 , and the addition circuit U 5  respectively have the same functions as the amplifier  51 , the A/D conversion circuit  52 , the quadrature detection circuit  53 , the reception delay circuit  54 , and the addition circuit  55 , shown in  FIG. 4 . Therefore, these explanations will be omitted. The filter processing circuit U 6  has a function of applying an arbitrary complex reception filter (including a real number reception filter) to the I/Q signal which is the output of the addition circuit U 5 , and a function of outputting the I/Q signal after the complex reception filter is applied to the B-mode processing circuit  12 , the Doppler processing circuit  13 , and the transmitting circuit  111 . 
     In the above description of the receiving circuit U, a case where the receiving circuit U has a configuration for performing I/Q beamforming will be described. In I/Q beamforming, an RF signal is orthogonally detected, converted into an I/Q baseband, and then delayed and added to generate an ultrasonic image. However, it is not limited to that case. The receiving circuit U may have a configuration for performing RF beamforming. In RF beamforming, after delay addition of RF signals, quadrature detection is performed and converted into I/Q signals composed of I signal and Q signal to generate an ultrasonic image. 
     The transmitting circuit  111  includes a pulse generating circuit  61 , a transmission delay circuit  62 , a drive circuit  63 , an evaluating circuit  64 , and a frequency setting circuit  65 . The evaluating circuit  64  may be provided in the B-mode processing circuit  12  (or the Doppler processing circuit  13 ) instead of the T/R circuit  11 . 
     The pulse generating circuit  61  repeatedly generates a rate pulse for forming a transmission ultrasonic wave at a predetermined rate frequency under the control of the processing circuitry  17 . 
     The transmission delay circuit  62  converges the ultrasonic waves generated from the ultrasonic transducer of the ultrasonic probe  20  into a beam shape, and gives a delay time of each piezoelectric transducer necessary for determining the transmission directivity to each rate pulse generated by the pulse generating circuit  61  under the control of the processing circuitry  17 . 
     The drive circuit  63  applies a drive pulse to the ultrasonic transducer at a timing based on the rate pulse under the control of the processing circuitry  17 . The drive circuit  63  is one example of a drive unit. 
     In the embodiment, the transmission frequency (lowest frequency/medium frequency/highest frequency) of the ultrasonic wave transmitted from the ultrasonic probe  20  can be selected by a user interface (UI). However, optimization of transmission frequency selection including sensitivity is desired. This is because there may be an operator who does not even touch the UI, or the operator may not have the skill to select an appropriate transmission frequency. Therefore, the transmitting circuit  111  provided in the T/R circuit  11 A has the evaluating circuit  64  and the frequency setting circuit  65 . As a result, the degree of beam penetration to the deep portion is evaluated as the sensitivity, and an appropriate transmission frequency is automatically selected according to the degree of beam penetration to the deep portion. Here, the lowest frequency is also called “PEN: Penetration”. The medium frequency is also called “GEN: general”. The highest frequency is also called “RES: Resolution”. 
     Under the control of the processing circuitry  17 , the evaluating circuit  64  analyzes the received signal at a predetermined depth based on the received signal of the ultrasonic wave, and evaluates the degree of beam penetration to the deep portion. For example, the evaluating circuit  64  evaluates degree of beam penetration to the deep portion using the signal to noise (SN) ratio of the deep determination region described later. It is based on B-mode data (or Doppler data) as raw data from the B-mode processing circuit  12  (or Doppler processing circuit  13 ). The evaluating circuit  64  may analyze the received signal having a predetermined depth based on the B-mode image data (or Doppler image data) after scan conversion from the image generating circuit  14 . The evaluating circuit  64  is one example of an evaluating unit. 
     The frequency setting circuit  65  sets the transmission frequency based on the result of the evaluating circuit  64  under the control of the processing circuitry  17 . As a result, the drive circuit  63  can generate a drive pulse based on the transmission frequency set by the frequency setting circuit  65 , and apply the drive pulse to the ultrasonic transducer of the ultrasonic probe  20  at a timing based on the rate pulse. The frequency setting circuit  65  is one example of the frequency setting unit. 
     Subsequently, an operation of the ultrasonic diagnostic apparatus  10 A will be described. The ultrasonic diagnostic apparatus  10 A samples at a low transmission frequency (for example, the lowest frequency (PEN) of the switchable transmission frequencies), and controls to switch to a high transmission frequency (for example, medium frequency (GEN)) when the SN ratio of the image has a margin. 
     Each of  FIGS. 15 and 16  is a diagram showing an operation of the ultrasonic diagnostic apparatus  10 A as a flowchart. In  FIGS. 15 and 16 , the reference numerals “ST” with numbers indicate each step of the flowchart. Note that, in  FIGS. 15 and 16 , the case of I/Q beamforming, that is, the case where the reception filter is a complex reception filter will be described as an example. 
     As shown in  FIG. 15 , the processing circuitry  17  of the ultrasonic diagnostic apparatus  10 A controls the T/R circuit  11 A and the like to start an ultrasonic scan using the ultrasonic probe  20  (step ST 21 ). The T/R circuit  11 A controls the ultrasonic probe  20  by a drive pulse having a low transmission frequency (e.g., the lowest frequency (PEN)) set by the frequency setting circuit  65  to transmit/receive ultrasonic waves (step ST 22 ). The filter processing circuit U 6  acquires the I/Q signal for one frame which is the output of the addition circuit U 5  (step ST 23 ). 
     The filter processing circuit U 6  applies an arbitrary complex reception filter to the I/Q signal for one frame acquired in step ST 23  (step ST 24 ). The B-mode processing circuit  12  generates B-mode data as raw data for one frame based on the I/Q signal to which an arbitrary complex reception filter is applied in step ST 24  (step ST 25 ). 
     In steps ST 26  to ST 31 , the evaluating circuit  64  analyzes the received signal at a predetermined depth to evaluate the degree of beam penetration to the deep portion. First, the evaluating circuit  64  divides the image region formed by the B-mode data for one frame generated in step ST 25  into multiple divided regions such that each region has multiple pixels (step ST 26 ). The evaluating circuit  64  calculates the SN ratio of each divided region after division and the variance of the signals in step ST 26  based on the B-mode data for one frame generated in step ST 25  (step ST 27 ).  FIG. 17  shows 4×8 divided regions in the image region formed by one frame of B-mode data. Each divided region contains N (N: an integer greater than or equal to 2) pixels. 
     In step ST 27 , the evaluating circuit  64  acquires the signal mean of each divided region by the following equation (1) (signal mean). It is based on the average of multiple signals corresponding to the respective multiple pixels in each divided area. In step ST 27 , the evaluating circuit  64  acquires the noise mean of each divided region by the following equation (2). It is based on the average of multiple noises corresponding to the respective multiple pixels in each divided region. Then, in step ST 27 , the evaluating circuit  64  calculates the SN ratio (SNR) [dB] of each divided region by the following equations (3) and (4). It is based on the signal average and noise average of multiple pixels in each divided area. Further, in step ST 27 , the evaluating circuit  64  calculates the variance (Var) of each divided region by the following equation (5). It is based on multiple signals corresponding to the respective pixels in each divided region and a signal mean of each divided region. 
     
       
         
           
             
               
                 
                   
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     The evaluating circuit  64  determines whether or not the SN ratio of the shallow determination region in the image region formed by the B-mode data for one frame is equal to or greater than the first threshold value (step ST 28 ). The I/Q signal that is the basis of the B-mode data includes a received signal in a scanned state or a received signal in an aerial state in which the ultrasonic probe  20  is left in the air away from the body surface of the subject. The state in which the ultrasonic probe  20  is left in the air away from the body surface of the subject is synonymous with the state in which ultrasonic waves are not transmitted to the subject. Therefore, in step ST 28 , the evaluating circuit  64  does not evaluate the degree of beam penetration to the deep portion when the ultrasonic probe  20  is left in the air. 
       FIG. 17  is a diagram showing an example of a shallow determination region set in the image region formed by B-mode data for one frame. 
     As shown in  FIG. 17 , the image region formed by the B-mode data for one frame has a total of 32 divided regions having 8 steps in the depth direction (i) and 4 rows in the beam direction j. The evaluating circuit  64  sets the determination region Su in a shallow portion of the image region. Here, among the image regions, the shallow determination region Su is set in the third and fourth stages from the top, and eight shallow divided regions corresponding to the shallow portion are set. 
     The evaluating circuit  64  evaluates the signal to noise ratio in the eight shallow divided regions, and determines whether the ultrasonic probe  20  is in a scanning state of being applied to the body surface of the subject or is in an aerial state where the ultrasonic probe  20  is away from the body surface of the subject. When the SN ratio of at least one shallow divided region out of the eight shallow divided regions is equal to or greater than the first threshold value, the evaluating circuit  64  may determine that the scan state is in effect. Alternatively, the evaluating circuit  64  may determine that it is in the scan state only when the SN ratios of all the eight shallow divided regions are equal to or higher than the first threshold value. Alternatively, the evaluating circuit  64  may set only one divided region as the shallow divided region, and may determine that the scan state is in the scan state when the SN ratio of the shallow divided region is equal to or greater than the first threshold value. 
     Returning to the description of  FIG. 15 , if it is determined as “NO” in step ST 28 , that is, if it is determined that the SN ratio of the shallow determination region in the image region is less than the first threshold value, the process proceeds to step ST 36  (in  FIG. 16 ). That is, the frequency setting circuit  65  does not change the transmission frequency when the SN ratio in the shallow determination region is less than the first threshold value. On the other hand, if it is determined as “YES” in step ST 28 , that is, if it is determined that the SN ratio of the shallow determination region in the image region is equal to or higher than the first threshold value, the evaluating circuit  64  determines that the scan state is in effect, and determines the structure or parenchyma of each divided region (step ST 29 ). In the embodiment, the parenchyma refers to an organ such as a liver. 
     In step ST 29 , the evaluating circuit  64  determines whether each of the 4×8 divided regions is a structure or a parenchyma. This is because the presence of a structure having high brightness makes it difficult to evaluate the degree of beam penetration to the deep portion. If it is a case where: the SN ratio of each divided region is equal to or greater than the first threshold value; and the variance of the divided region is equal to or greater than the second threshold value, the evaluating circuit  64  determines that such a divided region corresponds to the structure. If it is a case where: the SN ratio of each divided region is equal to or greater than the first threshold; the variance of the divided region is less than the second threshold; and the variance of the divided region is equal to or greater than the third threshold (third threshold&lt;second threshold), the evaluating circuit  64  determines that such a divided region corresponds to the parenchyma. On the other hand, if it is a case where the SN ratio of each divided region is less than the first threshold value, or where the variance of each divided region is less than the third threshold, the evaluating circuit  64  determines that such a divided region does not correspond to the structure or the parenchyma. 
       FIG. 18  is a diagram for explaining a method of determining the structure and the parenchyma based on B-mode data for one frame. 
     The leftmost end of  FIG. 18  shows B-mode data as raw data for one frame. The second from the left shows the distribution of the SN ratio in the 4×8 divided regions. Each divided region is colored by the color arrangement bar Bl according to the magnitude of the SN ratio. The third from the left shows the distribution of the variance of the signals in each of the 4×8 divided regions. Each divided region is colored by the color arrangement bar B 2  according to the magnitude of the variance of the signals. 
     The second from the right in  FIG. 18  shows a divided region determined to be a structure in the B-mode data. These divided regions have a relatively large signal to noise ratio and a relatively large signal dispersion. The rightmost end of  FIG. 18  shows a divided region determined to be substantial in the B-mode data. These divided regions have a relatively large signal to noise ratio, while the variance of the signals is relatively small. The evaluating circuit  64  may display the distribution of the SN ratio and the distribution of the variance shown in  FIG. 18  on the display  40  at an arbitrary timing. 
     Proceeding to the description of  FIG. 16 , the evaluating circuit  64  determines whether or not the parenchyma determined by step ST 29  exists in the deep determination region of the image region formed by the B-mode data for one frame (Step ST 30 ). If it is determined as “YES” in step ST 30 , that is, if it is determined that the parenchyma exists in the deep determination region of the image region formed by one frame of B-mode data, the evaluating circuit  64  determines the SN of the deep determination region. It is determined whether or not the ratio is equal to or greater than the fifth threshold value (step ST 31 ). In step ST 27  (shown in  FIG. 15 ), the evaluating circuit  64  calculated the SN ratio and the signal variance for all of the divided regions, but the present invention is not limited to that case. For example, steps ST 28  to ST 30  may be omitted. In this case, in step ST 27 , the evaluating circuit  64  may calculate only the SN ratio for only the divided region belonging to the deep determination region among the divided regions for step ST 31 . 
       FIG. 19  is a diagram showing an example of a deep determination region set in the image region formed by B-mode data for one frame.  FIG. 19  is a diagram showing steps ST 30  and ST 31 . 
     As shown in  FIG. 19 , the evaluating circuit  64  sets a deep determination region Sb in the deep portion of the image region formed by the B-mode data for one frame. Here, in the image region, the deep determination region Sb is set in the lowermost two stages, and eight deep divided regions corresponding to the deep portion are set. In step ST 30 , the evaluating circuit  64  determines that three of the eight deep divided regions belonging to the determination region Sb belong to the parenchyma. 
     Then, in step ST 31 , the evaluating circuit  64  evaluates the SN ratio in the three deep divided regions belonging to the parenchyma among the eight deep divided regions. The evaluating circuit  64  may determine whether or not the average of the three SN ratios corresponding to the three deep divided regions belonging to the parenchyma is equal to or greater than the fifth threshold value. The evaluating circuit  64  may determine whether or not the average of the eight SN ratios corresponding to all eight deep divided regions is equal to or greater than the fifth threshold value. 
     Returning to the explanation of  FIG. 16 , if it is determined as “YES” in step ST 31 , that is, if it is determined that the SN ratio of the deep determination region in the B-mode data region for one frame is equal to or higher than the fifth threshold value, the frequency setting circuit  65  determines that the degree of beam penetration to the deep portion is high for the B-mode data for the one frame. Then, the frequency setting circuit  65  sets the transmission frequency higher than that set in step ST 22 , and switches to a higher transmission frequency (step ST 32 ). This is because when the degree of beam penetration to the deep portion is high, even if the transmission frequency is changed to a high value, the effect on the deep imaging is considered to be small. 
     If it is determined as “NO” in step ST 30 , or if it is determined as “NO” in step ST 31 , the T/R circuit  11 A does not change the transmission frequency set by the frequency setting circuit  65 . The T/R circuit  11 A controls the ultrasonic probe  20  by a drive pulse having a low transmission frequency similar to step ST 22  (shown in  FIG. 15 ) to transmit/receive ultrasonic waves (step ST 33 ). On the other hand, the T/R circuit  11 A controls the ultrasonic probe  20  by the drive pulse of the high transmission frequency after switching in step ST 32  to transmit/receive ultrasonic waves (step ST 33 ). The filter processing circuit U 6  acquires the I/Q signal for one frame which is the output of the addition circuit U 5  (step ST 34 ). 
     The filter processing circuit U 6  applies an arbitrary complex reception filter to the I/Q signal for one frame acquired in step ST 34  (step ST 35 ). The B-mode processing circuit  12  (or Doppler processing circuit  13 ) and the image generating circuit  14  generate an ultrasonic image based on the I/Q signal for one frame to which the complex reception filter is applied in step ST 35  (step ST 36 ). An ultrasonic image for one frame is generated based on the I/Q signal for one frame to which the complex reception filter is applied acquired in step ST 24  or ST 35  (step ST 36 ). 
       FIG. 20  is a diagram showing an ultrasonic image when the transmission frequency is controlled.  FIG. 20A  shows a B-mode image in the case of a low transmission frequency, for example, the lowest frequency (PEN).  FIG. 20B  shows a B-mode image for high transmission frequencies, for example, the medium frequency (GEN). The imaging target (site) of the B-mode image shown in  FIG. 20  is the liver. 
     In the B-mode image shown in  FIG. 20A  based on the transmission and reception of ultrasonic waves having the lowest frequency, even the form of the deep portion can be sufficiently visually recognized. However, if the transmission frequency is arbitrarily switched from the lowest frequency to the medium frequency or the highest frequency, as shown in  FIG. 20B , the degree of beam penetration to the deep portion becomes low, and it becomes difficult to visually recognize the deep portion. Therefore, the ultrasonic diagnostic apparatus  10 A evaluates the degree of beam penetration to the deep portion from the B-mode image based on the ultrasonic transmission/reception of the lowest frequency, thereby switching the transmission frequency from the lowest frequency to the medium frequency or from the medium frequency to the highest frequency. 
     Returning to the description of  FIG. 16 , the processing circuitry  17  determines whether or not to finish the ultrasonic scan started by step ST 21  (shown in  FIG. 15 ) (step ST 37 ). For example, the processing circuitry  17  determines whether or not to finish the ultrasonic scan by the finish operation by the operator via the input interface  30 . If it is determined as “NO” in step ST 37 , that is, if it is determined that the ultrasonic scan started in step ST 21  is not finished, the process proceeds to the next frame (step ST 38 ), and the T/R circuit  11 A controls the ultrasonic probe  20  by a drive pulse having a low or high transmission frequency after being switched to transmit/receive ultrasonic waves (step ST 33 ). 
     On the other hand, If it is determined as “YES” in step ST 37 , that is, if it is determined that the ultrasonic scan started in step ST 21  is finished, the processing circuitry  17  of the ultrasonic diagnostic apparatus  10 A controls the T/R circuit  11 A and the like to finish the ultrasonic scan using the ultrasonic probe  20 . The processing circuitry  17  can display the ultrasonic image (e.g., B-mode image) generated in step ST 36  on the display  40 . Further, the processing circuitry  17  can also display the ultrasonic images before and after the switching of the transmission frequency on the display  40  in parallel. Further, the processing circuitry  17  can also display a message on the display  40  with respect to the ultrasonic image after the transmission frequency is switched. The message is for the operator to select the transmission frequency after switching as it is. 
     Therefore, when the transmission frequency set in step ST 22  is the lowest frequency (PEN), the transmission frequency after switching in step ST 32  is the medium frequency (GEN) or the highest frequency (RES). When the transmission frequency set in step ST 22  is the lowest frequency (PEN), and when the transmission frequency after switching in step ST 32  is the highest frequency (RES), it is determined whether or not the SN ratio of the deep determination region is equal to or greater than the sixth threshold value (sixth threshold value&gt;fifth threshold value). Alternatively, when the transmission frequency set in step ST 22  is the medium frequency, the transmission frequency after switching in step ST 32  is the highest frequency. 
     Further, the transmission frequency may be switched stepwise. For example, the transmission frequency is set to the lowest frequency (step ST 22 ). When the SN ratio in the deep determination region is equal to or greater than the fifth threshold value, the transmission frequency is switched from the lowest frequency to the higher medium frequency (step ST 32 ). Subsequently, the transmission frequency is set to the medium frequency after switching (step ST 22 ), and it is determined whether the SN ratio of the deep determination region is equal to or higher than the fifth threshold value. Then, when the SN ratio in the deep determination region is equal to or higher than the fifth threshold value, the transmission frequency is switched from the medium frequency to the high maximum frequency (step ST 32 ). 
     In the above description, it has been described that the evaluation by step ST 26  is started immediately after the start of the ultrasonic scan by step ST 21 , but the present invention is not limited to this case. For example, the evaluation starting from step ST 26  may be triggered in: change in the position or angle of the ultrasonic probe  20  during ultrasonic scanning; change of information of ultrasonic images (scan conditions such as display depth); and scan-hold operation. Further, the evaluation target is not limited to the raw data acquired live, and may be the raw data of the past image. 
     Further, the ultrasonic images corresponding to the transmission frequencies are generated according to the flowcharts shown in  FIGS. 15 and 16 , thereby the processing circuitry  17  may arrange the ultrasonic images in descending order of the deep SN ratio and display them on the display  40 . In this case, the operator selects a predetermined ultrasonic image, and the frequency setting circuit  65  sets the transmission frequency at which the ultrasonic image is acquired. 
     As described above, according to the ultrasonic diagnostic apparatus  10 A, it is possible to suppress deterioration of image quality due to ultrasonic attenuation by controlling the transmission frequency according to the degree of beam penetration to the deep portion. Thereby, it is possible to provide a high-quality ultrasonic image. 
     6. Modification 
     In the ultrasonic diagnostic apparatus  10 A, the transmission frequency is switched from the low transmission frequency to the high transmission frequency when the SN ratio of the deep determination region at the low transmission frequency is equal to or higher than the second threshold value. However, it is not limited to that case. For example, when the SN ratio of the deep determination region at a high transmission frequency is less than the fifth threshold value, the ultrasonic diagnostic apparatus  10 A may determine that the degree of beam penetration to the deep portion is low, and may switch the transmission frequency from a high transmission frequency to a low transmission frequency. However, if simple and highly reproducible transmission frequency control is desired without considering the difference between each test of the subject, it is preferable to control the transmission frequency from a low transmission frequency to a high transmission frequency. 
     7. Ultrasonic Diagnostic Apparatus According to Third Embodiment 
     The above-mentioned ultrasonic diagnostic apparatus realizes the provision of high-quality ultrasonic images by controlling the transmission frequency of ultrasonic waves or controlling a complex reception filter. However, it may be possible to provide a high-quality ultrasonic image by both controlling the transmission frequency of the ultrasonic wave and controlling the complex reception filter. That is, the above-mentioned first and second embodiments may be combined. A case will be described below as an ultrasonic diagnostic apparatus according to a third embodiment. 
       FIG. 21  is a schematic diagram showing a configuration of an ultrasonic diagnostic apparatus according to a third embodiment. 
       FIG. 21  shows the ultrasonic diagnostic apparatus  10 B according to the third embodiment. Further,  FIG. 21  shows an ultrasonic probe  20 , an input interface  30 , and a display  40 . A device in which at least one of the ultrasonic probe  20 , the input interface  30 , and the display  40  is added to the ultrasonic diagnostic apparatus  10  B may be referred to as “ultrasonic diagnostic apparatus”. In the following description, a case where the ultrasonic probe  20 , the input interface  30 , and the display  40  that are all provided outside the ultrasonic diagnostic apparatus  10 B will be described. 
     The ultrasonic diagnostic apparatus  10 B includes a T/R circuit  11 B, a B-mode processing circuit  12 , a Doppler processing circuit  13 , an image generation circuit  14 , an image memory  15 , a network interface  16 , a processing circuitry  17 , and a main memory  18 . The circuits  11 B,  12  to  14  are configured by an integrated circuit for a specific application or the like. However, the present invention is not limited to this case, and all or a part of the functions of the circuits  11 B,  12  to  14  may be realized by the processing circuitry  17  executing the program. 
     In  FIG. 21 , the same parts as those shown in  FIG. 1  are designated by the same reference numerals, and the description thereof will be omitted. 
     The T/R circuit  11 B includes a transmitting circuit  111  and a receiving circuit  112  (shown in  FIG. 22 ). The T/R circuit  11 B controls the transmission directivity and the reception directivity in the transmission/reception of ultrasonic waves under the control of the processing circuit  17 . A case where the T/R circuit  11 B is provided in the ultrasonic diagnostic apparatus  10 B will be described. However, the T/R circuit  11 B may be provided in the ultrasonic probe  20 , or may be provided in both the ultrasonic diagnostic apparatus  10 B and the ultrasonic probe  20 . The T/R circuit  11  B is one example of a transmitter-and-receiver. 
       FIG. 22  is a block diagram showing a configuration of the T/R circuit  11 B. 
       FIG. 22  shows a transmitting circuit  111  and a receiving circuit  112  provided in the T/R circuit  11 B. The transmitting circuit  111  includes a pulse generating circuit  61 , a transmission delay circuit  62 , and a drive circuit  63 , an evaluating circuit  64  and frequency setting circuit  65 , and supplies a drive signal to the ultrasonic transducer of the ultrasonic probe  20 . The receiving circuit  112  includes an amplifier  51 , an A/D conversion circuit  52 , a quadrature detection circuit  53 , a reception delay circuit  54 , an addition circuit  55 , a filter processing circuit  56 , a frequency characteristic analysis circuit  57  and a filter setting circuit  58 , and receives the echo signal received by the ultrasonic transducer and performs various processing on the echo signal to generate echo data. All the functions of circuits  61  to  65  and  51  to  58  are realized by one processing circuit executing a program, or some of them may be realized by executing programs by different processing circuits. 
     In the transmitting circuit  111  of  FIG. 22 , the same members as those of the transmitting circuit  111  shown in  FIG. 14  are designated by the same reference numerals, and the description thereof will be omitted. Further, in the receiving circuit  112  of  FIG. 22 , the same members as those of the receiving circuit  112  shown in  FIG. 4  are designated by the same reference numerals, and the description thereof will be omitted. 
     Subsequently, the operation of the ultrasonic diagnostic apparatus  10  B will be described. It should be noted that it is possible to select with a preset whether to control only the ultrasonic transmission frequency, or only the complex reception filter, or both. 
     Each of  FIGS. 23 and 24  is a diagram showing an operation of the ultrasonic diagnostic apparatus  10  B as a flowchart. In  FIGS. 23 and 24 , the reference numerals “ST” with numbers indicate each step of the flowchart. In addition, in  FIG. 23  and  FIG. 24 , the case of I/Q beamforming, that is, the case where the reception filter is a complex reception filter will be described as an example. Further, in  FIGS. 23 and 24 , the same steps as the steps in the flowcharts of  FIGS. 15 and 16  are designated by the same reference numerals, and the description thereof will be omitted. 
     As shown in  FIG. 23 , after the ultrasonic scan is started (step ST 21 ), the processing circuitry  17  of the ultrasonic diagnostic apparatus  10  B determines whether or not to control the transmission frequency (step ST 51 ). For example, the processing circuitry  17  determines whether or not to control the transmission frequency by the finish operation by the operator via the input interface  30 . If it is determined as “YES” in step ST 51 , that is, if it is determined that the transmission frequency is controlled, the T/R circuit  11 B controls the ultrasonic probe  20  by the drive pulse of the low transmission frequency set by the frequency setting circuit  65 , and transmits/receives ultrasonic waves (step ST 22 ). 
     On the other hand, if it is determined as “NO” in step ST 51 , that is, the transmission frequency is not controlled, the process proceeds to step ST 33  shown in  FIG. 24 . 
     Proceeding to the description of  FIG. 24 , ultrasonic waves are transmitted and received by a drive pulse corresponding to a low or high transmission frequency after switching, then the processing circuitry  17  of the ultrasonic diagnostic apparatus  10  B determines whether or not to control the complex reception filter (step ST 52 ). For example, the processing circuitry  17  determines whether or not to control the complex reception filter by the finish operation by the operator via the input interface  30 . 
     If it is determined as “YES” in step ST 52 , that is, if it is determined that the complex reception filter is controlled, the process proceeds to step ST 2  in  FIG. 5 . On the other hand, if it is determined as “NO” in step ST 52 , that is, if it is determined that the complex reception filter is not controlled, the process proceeds to step ST 34   
     in  FIG. 16 . With ultrasonic diagnostic apparatus  10 B, any one of: the case where only controlling the complex reception filter (first embodiment); the case where only controlling the transmission frequency (second embodiment); and the case where controlling both the complex reception filter and controlling the transmission frequency can be selected arbitrarily. If it is determined as “NO” in step ST 51  and as “YES” in step ST 52 , the ultrasonic diagnostic apparatus  10  B can only control the complex reception filter. If it is determined as “YES” in step ST 51  and as “NO” in step ST 52 , the ultrasonic diagnostic apparatus  10 B can only control the transmission frequency. If it is determined as “YES” in step ST 51  and as “YES” in step ST 52 , the ultrasonic diagnostic apparatus  10 B can control both the complex reception filter and the transmission frequency. 
     Each of  FIGS. 25A and 25B  is a diagram showing an ultrasonic image when the transmission frequency and the complex reception filter are controlled.  FIG. 25A  shows a B-mode image in the case of a low transmission frequency, for example, the lowest frequency (PEN), and in the case of controlling the complex reception filter according to the depth.  FIG. 25B  shows a B-mode image in the case of a high transmission frequency, for example, a medium frequency (GEN), and in the case where the complex reception filter is controlled according to the depth. The imaging target (site) of the B-mode image shown in  FIG. 25  is the liver. 
     In  FIG. 25A , the image quality is optimized as compared with  FIG. 20A . Further, in the B-mode image shown in  FIG. 25A  based on the ultrasonic transmission/reception of the lowest frequency and to which the complex reception filter according to the depth is applied, even the form of the deep portion can be sufficiently visually recognized. On the other hand, if the transmission frequency is arbitrarily switched from the lowest frequency to the medium frequency or the highest frequency, as shown in  FIG. 25B , the degree of beam penetration to the deep portion becomes low, and it becomes difficult to visually recognize the deep portion. Therefore, the ultrasonic diagnostic apparatus  10 B evaluates the degree of beam penetration to the deep portion from the B-mode image based on the ultrasonic transmission/reception of the lowest frequency even when the complex reception filter according to the depth is applied. As a result, the ultrasonic diagnostic apparatus  10 B switches the transmission frequency from the lowest frequency to the medium frequency or from the medium frequency to the highest frequency. 
     When both the transmission frequency control and the complex reception filter control are performed, multiple transmission frequencies can be scanned. In that case, the degree of beam penetration to the deep portion is evaluated at each transmission frequency, and the transmission frequency when the deep SN ratio is the highest is adopted. This is to optimize the image quality condition in the desired reception band. 
     As described above, according to the ultrasonic diagnostic apparatus  10 B, the transmission frequency is controlled according to the degree of beam penetration to the deep portion, and the complex reception filter is controlled according to the depth. As a result, it is possible to suppress image quality deterioration due to ultrasonic attenuation. Thereby, it is possible to provide a high-quality ultrasonic image. Further, in the ultrasonic diagnostic apparatus  10 B, both the control of the ultrasonic transmission frequency (second embodiment) and the control of the complex reception filter (first embodiment) can be combined. Even when the transmission frequency is lowered to reduce the image quality when only the ultrasonic transmission frequency is controlled, it is possible to compensate the disadvantage by controlling the complex reception filter. 
     According to at least one embodiment described above, it is possible to suppress deterioration of image quality due to ultrasonic attenuation, so it is possible to provide a high-quality ultrasonic image. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, changes, and combinations of embodiments in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.