JP4713118B2 - Ultrasonic imaging device - Google Patents

Description

  The present invention relates to an ultrasonic imaging apparatus used for performing diagnosis and nondestructive examination of an organ in a living body by transmitting and receiving ultrasonic waves and displaying an ultrasonic image of a subject.

  In general, in an ultrasonic imaging apparatus such as an ultrasonic diagnostic apparatus or an industrial flaw detection apparatus, an ultrasonic probe (probe) including a plurality of ultrasonic transducers having an ultrasonic transmission / reception function is used. Using such an ultrasonic probe, the subject is scanned with an ultrasonic beam formed by combining a plurality of ultrasonic waves, and an ultrasonic echo reflected inside the subject is received. Thus, image information related to the subject is obtained based on the intensity of the ultrasonic echo. Furthermore, based on this image information, a two-dimensional or three-dimensional image relating to the subject is reproduced. As one of scanning methods using such an ultrasonic beam, so-called sector scanning is known in which a fan-shaped two-dimensional region of a subject is scanned.

  Sector scanning was originally developed as a technique for observing the heart from the intercostal space of the human body. In general, in sector scanning, a plurality of ultrasonic beams extending in the depth direction of a subject from a transmission point are sequentially transmitted in a fan shape into the subject, and by these ultrasonic beams, as shown in FIG. A fan-shaped two-dimensional region of the subject is scanned at equally spaced angles.

  When receiving an ultrasonic echo reflected from the subject, it is reflected from each of a plurality of sampling points distributed at equal intervals in the depth direction of the subject along each ultrasonic beam (sound ray). A phase matching process is performed on a plurality of reception signals based on the ultrasonic echoes to obtain an acoustic ray signal (scanning line signal) in which the focal points of the ultrasonic echoes are narrowed down. Further, the sound ray signal is detected and a process for converting the scanning method is performed, whereby an image signal for displaying an ultrasonic image on a normal display device is obtained. The ultrasound image obtained in this way is called a tomographic echocardiogram for the heart.

  However, in sector scanning, sound ray data is obtained by scanning a subject with an ultrasonic beam formed in a fan shape, so that the density of sound rays decreases as the depth of the subject increases. Therefore, in the deep part of the subject, there are problems that the resolution of the image is lowered and artifacts such as moire patterns are generated. In view of this, image quality deterioration is improved by interpolating image information between two adjacent sound rays.

The image information interpolation process will be described with reference to FIG. FIG. 6 shows two ultrasonic beams A and B, and pixels A1 to A5 and B1 to B1 are generated based on ultrasonic echoes generated by reflection of these ultrasonic beams at each part of the subject. Image information in B5 is obtained. However, since the image information at the pixel X through which the center of the ultrasonic beam does not pass is not obtained, the image information at the pixel X is interpolated using the image information at the pixels A2, A3, B2, and B3, for example. Details regarding the interpolation processing of image information are described in Non-Patent Document 1.

  As a related technique, the following Patent Document 1 discloses an acoustic imaging apparatus and a method for increasing the resolution without reducing the frame rate of the system. In this acoustic imaging apparatus, the signal processing order is changed in order to increase the resolution of the image by utilizing signal phase information that is normally lost during the reconstruction process. That is, the signal generated by the converter is detected and subjected to scan conversion or data interpolation before being processed with restrictions.

  Patent Document 2 below discloses that an ultrasonic diagnostic apparatus capable of receiving a plurality of directions improves the S / N ratio and obtains an image with high diagnostic ability. This ultrasonic diagnostic apparatus stores in a line memory a reception beam that overlaps after the movement of the transmission center among a plurality of reception beams obtained by one transmission, moves the transmission center so that the reception beams overlap, The overlapping reception beam and the reception beam stored in the previous line memory are processed by the averaging circuit, and this is sequentially stored in the frame memory to obtain one image. Thereby, the S / N ratio can be improved.

  Patent Document 3 below discloses an ultrasonic scanning conversion device capable of reproducing accurate luminance information of image data between a plurality of sampled points by calculation. In this ultrasonic scanning conversion device, the amount of change between sampled luminance information and sampled luminance information adjacent thereto is calculated and encoded, and this is added to the latter image information data. Then, the interpolation calculation means performs a proportional operation between the image information data to which the difference is added and the adjacent image information data, and corrects this by the sign of the encoded difference to approximate true luminance information. Data calculation between adjacent image data is performed.

In the above patent documents, the phase matching for narrowing the focal point of the ultrasonic echo and the scan conversion from the sound ray signal (scanning line signal) after the phase matching to the image signal for display are performed separately. Although the burden at the time of image signal generation is light, there is still room for improvement in image quality.
“Revised Medical Ultrasound Instrument Handbook” edited by Japan Electronic Machinery Manufacturers Association, Inc., Corona, Inc., published on April 20, 1985, p. 100-102 Japanese Patent No. 3408284 (page 3, FIG. 3) JP-A-8-38472 (pages 1 and 2, FIG. 1) Japanese Patent Laid-Open No. 3-162841 (pages 2 and 3, FIG. 1)

  Therefore, in view of the above points, the present invention provides an ultrasonic imaging apparatus capable of obtaining an ultrasonic image with improved image quality by effectively utilizing ultrasonic echo information obtained by transmitting and receiving ultrasonic waves. The purpose is to do.

In order to solve the above problems, an ultrasonic imaging apparatus according to the present invention forms an ultrasonic beam according to a plurality of drive signals and transmits the ultrasonic beam to a subject, and receives a plurality of ultrasonic echoes reflected from the subject. An ultrasonic probe including a plurality of ultrasonic transducers that respectively generate a received signal and a plurality of ultrasonic beams sequentially transmitted from the ultrasonic probe in a plurality of different transmission directions Transmitting means for supplying a plurality of driving signals to a plurality of ultrasonic transducers so as to scan over a scanning range of the plurality of ultrasonic signals, and a plurality of received signals obtained by receiving ultrasonic echoes by the plurality of ultrasonic transducers. by performing phase matching process for, generating a waveform signal representative of the waveform information of the ultrasonic echo in all the pixels included in the scanning range of the subject And査方type converting means, based on the waveform signals generated by the scanning system conversion means, and an image signal generating means for generating an image signal representing the luminance of all the pixels included in the scanning range of the subject, transmitting a plurality of different One type of image signal by combining a storage unit that stores a plurality of types of image signals generated by the image signal generation unit with respect to the direction, and an image represented by the plurality of types of image signals stored in the storage unit And an image composition means for obtaining.

According to the present invention, a phase matching process is performed on a plurality of reception signals obtained by a plurality of ultrasonic transducers receiving ultrasonic echoes, thereby performing supervision in all pixels included in the scan range of the subject. Since the waveform signal representing the waveform information of the sound echo is generated, the ultrasound echo information obtained by transmitting and receiving the ultrasound can be effectively utilized to obtain an ultrasound image with improved image quality.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a block diagram showing a configuration of an ultrasonic imaging apparatus according to an embodiment of the present invention. The ultrasonic imaging apparatus includes an ultrasonic probe (probe) 1 used in contact with a subject, and an ultrasonic imaging apparatus main body 2 connected to the ultrasonic probe 1. An ultrasonic beam is transmitted from the ultrasonic probe 1 toward the subject, and an ultrasonic echo reflected from the subject is received to generate an ultrasonic image.

  The ultrasonic probe 1 includes a plurality of ultrasonic transducers 11 a constituting a one-dimensional or two-dimensional transducer array (also referred to as “array transducer”) 11. These ultrasonic transducers 11a are connected to the ultrasonic imaging apparatus body 2 via signal lines.

  Each of the ultrasonic transducers 11a includes, for example, a piezoelectric ceramic represented by PZT (Pb (lead) zirconate titanate) or a polymer piezoelectric element represented by PVDF (polyvinylidene difluoride). It is comprised by the vibrator | oscillator which formed the electrode at both ends of the material (piezoelectric body) which has piezoelectricity, such as. In addition, in recent years, a piezoelectric material containing PZNT (an oxide containing lead, zinc, niobium, titanium), which is expected to contribute to the improvement of sensitivity and bandwidth of an ultrasonic transducer, may be used.

  When a voltage is applied to the electrodes of such a vibrator by sending a pulsed or continuous wave electric signal, the piezoelectric body expands and contracts. By this expansion and contraction, pulsed or continuous wave ultrasonic waves are generated from the respective vibrators, and an ultrasonic beam is formed by synthesizing these ultrasonic waves. Each vibrator expands and contracts by receiving propagating ultrasonic waves and generates an electrical signal. These electrical signals are output as received signals.

The ultrasonic imaging apparatus main body 2 includes a plurality of switching circuits 20, a plurality of transmission circuits 21, a plurality of reception circuits 22, a computer 30, a recording unit 40, and a display unit 50.
The plurality of switching circuits 20 respectively connect a plurality of ultrasonic transducers 11a built in the ultrasonic probe 1 to the plurality of transmission circuits 21 when transmitting ultrasonic waves, and when receiving ultrasonic waves, A plurality of ultrasonic transducers 11a are connected to a plurality of receiving circuits 22, respectively.

  Each of the plurality of transmission circuits 21 includes a D / A converter and a class A power amplifier. The D / A converter generates a drive signal having a delay amount corresponding to the transmission direction of the ultrasonic beam based on the waveform data supplied from the computer 30. The power amplifier amplifies this drive signal and supplies it to the ultrasonic probe 1.

  Each of the plurality of receiving circuits 22 includes a preamplifier and an A / D (analog / digital) converter. The reception signal output from each ultrasonic transducer 11a is amplified by a preamplifier and converted into a digital signal by an A / D converter. The sampling frequency of the A / D converter needs to be at least about 10 times the frequency of the ultrasonic wave, and is preferably 16 times or more the frequency of the ultrasonic wave. The resolution of the A / D converter is preferably 10 bits or more.

  The computer 30 controls transmission / reception of ultrasonic waves based on software (control program) recorded in the recording unit 40. As the recording unit 40, a recording medium such as a hard disk, a flexible disk, MO, MT, RAM, CD-ROM, or DVD-ROM can be used. By the computer 30 and software, a scanning control unit 31, a waveform data generation unit 32, a scanning method conversion unit 35, an image data generation unit 36, an image composition unit 38, and an image processing unit 39 are function blocks. Realized. The computer 30 includes a transmission memory 33, a reception memory 34, and a plurality of image memories 37.

  The scanning control unit 31 sequentially sets the transmission direction of the ultrasonic beam, the reception direction and the focal position of the ultrasonic echo. The waveform data generation unit 32 sequentially reads the waveform data stored in the transmission memory 33 under the control of the scanning control unit 31 and outputs the waveform data to the plurality of transmission circuits 21. These transmission circuits 21 respectively generate a plurality of drive signals based on the waveform data, and supply them to the plurality of ultrasonic transducers 11 a included in the ultrasonic probe 1.

On the other hand, the reception memory 34 stores digital reception signals output from the A / D converters of the plurality of reception circuits 22 in time series for each ultrasonic transducer. The scanning method conversion unit 35 performs a phase matching process on the plurality of reception signals stored in the reception memory 34, so that a waveform signal representing waveform information of ultrasonic echoes in all the pixels to be displayed on the display device. Is generated. In this way, the reception signal of the R-θ coordinate obtained by scanning the subject according to the sector scan method is converted into the waveform signal of the XY coordinate according to the scanning method used in a normal display device.

  The image signal generation unit 36 generates an image signal representing the luminance at a plurality of pixels to be displayed on the display device, based on the waveform signal generated by the scanning method conversion unit 35. For example, the image signal generation unit 36 generates the image signal by obtaining the effective value of the waveform represented by the waveform signal or detecting the envelope of the waveform represented by the waveform signal. Furthermore, the image signal generation unit 36 may perform logarithmic compression processing on the generated image signal.

  The plurality of image memories 37 respectively store a plurality of types of image signals generated by the image signal generation unit 36 for a plurality of different transmission directions. For example, the first image memory 37 stores the first image signal generated for the first transmission direction. Similarly, the second image memory 37 stores the second image signal generated for the second transmission direction.

  The image synthesizing unit 38 obtains one type of image signal by synthesizing images represented by a plurality of types of image signals respectively stored in the plurality of image memories 37. At that time, the image composition unit 38 may add and average a plurality of luminance values respectively represented by a plurality of types of image signals respectively stored in the plurality of image memories 37, or may be used for weighting. The luminance value may be multiplied by a predetermined coefficient and added, or one type of image signal may be obtained by combining a plurality of types of image signals each representing an image of a plurality of sections constituting one screen.

  The image processing unit 39 performs image processing such as gradation processing and contour enhancement processing on the image signal output from the image synthesis unit 38 as necessary. The display unit 50 includes, for example, a display device such as a CRT or LCD, and displays an ultrasonic image based on the image signal output from the image processing unit 39.

Next, the operation of the ultrasonic imaging apparatus according to this embodiment will be described.
FIG. 2 is an enlarged view of the transducer array shown in FIG. The transducer array 11 includes N ultrasonic transducers (hereinafter also referred to as “elements”). Here, the X axis is taken along the vibration surfaces of the N elements, and the Y axis is taken at the center of the transducer array 11 so as to be orthogonal to the plane including these vibration surfaces.

Also, represents the channel number of each element in ch, the position vector of the elements of the channel number ch and a (ch), the position vector of the point P in the inner portion of the subject and an ultrasonic beam is transmitted is denoted by r The order of the transmission direction when transmitting the ultrasonic beam while changing the transmission direction is nTx. When an ultrasonic beam is transmitted only once in one direction, nTx corresponds to the number of transmissions, and this case will be described below.

Here, the time discretized at the time interval Δt is represented by i, and the time-varying waveform of the received signal obtained by the nTx-th transmission using the element of the channel number ch is s (ch, nTx, i). The echo waveform from the direction of the point P (position vector r) obtained by the nTx-th transmission is defined as e (r, i, nTx), and the echo intensity (luminance value) at the point P obtained by the nTx-th transmission. B (r, nTx) is given to the received signal from the element of channel number ch when the phase matching process is performed on a plurality of received signals based on the ultrasonic echoes from the point P direction. The delay amount is i _OFF (ch, r), and the weighting coefficient for performing the phase matching process is w (ch, nTx).

式（１）において、遅延量ｉ_ＯＦＦ（ｃｈ，ｒ）は、次式（２）によって与えられる。

式（２）において、記号ｃは、被検体中における超音波の音速を示している。 The scanning method conversion unit 35 performs phase matching using the following equation (1), and thereby represents a waveform representing the echo waveform e (r, i, nTx) from the point P direction based on the time-varying waveform of the received signal. Generate a signal.

In the equation (1), the delay amount i _OFF (ch, r) is given by the following equation (2).

In equation (2), the symbol c indicates the sound speed of the ultrasonic wave in the subject.

  The point P (position vector r) represents the position (X, Y) of a pixel used in a normal display device, and therefore, the R-θ coordinate obtained by scanning the subject according to the sector scan method. The received signal is converted into an XY coordinate waveform signal in accordance with a scanning method used in a normal display device.

Here, the scan mode conversion unit 35 based on the plurality of received signals obtained for one transmission direction, one of which represents the waveform information of the ultrasonic echo for each of all the pixels included in the scanning range of the subject Generate a waveform signal. Accordingly, a plurality of types of waveform signals are generated for a plurality of transmission directions. Since the point P (position vector r) represents the position (X, Y) of each pixel to be displayed on the display device, the scanning method conversion unit 35 performs interpolation processing on the waveform signal. Without, waveform signals can be generated for all pixels included in the scan range of the subject .

The image signal generation unit 36 uses the following equation (3), and based on the waveform signal generated by the scanning method conversion unit 35, the echo intensity serving as the base of the luminance values in a plurality of pixels to be displayed on the display device An image signal representing b (r, nTx) is generated.
b (r, nTx) = function {r, e (r, i, nTx)} (3)
Here, various methods can be used as a method for obtaining the echo intensity from the echo waveform (corresponding to the function function), and an example thereof will be described with reference to FIG.

  FIG. 3 shows the correspondence between the echo waveform and the image information in this embodiment. The image signal generation unit 36 is a time for cutting out a part of the waveform based on the position vector r of the point P with respect to the waveform signal representing the echo waveform e (r, nTx, i) in the nTx-th transmission. A window (range TRx) is set, and an effective value of the echo waveform in the range TRx is obtained and set as an echo intensity b (r, nTx) that is a base of the luminance value. FIG. 3 shows an enlarged view of an echo waveform in the range TRx and a position on the screen of image information obtained from the waveform in the range TRx.

In this way, one type of image signal representing one screen is obtained by repeating reception of ultrasonic waves and signal processing along the depth direction of the subject. Considering this corresponding to the scanning region in the subject, first, an ultrasonic beam is transmitted in the first transmission direction, and ultrasonic reception and signal processing are performed along the depth direction of the subject. by repeating, as shown in (a) in FIG. 4, a plurality (e.g., 5-7 lines) luminance in section S ₁ including the scanning lines of the first image signal is obtained bright. In the first image signal, the portion other than the section S _1, unless a strong reflection source, a dark image.

Next, the transmission direction is changed, the ultrasonic beam is transmitted in the second transmission direction, and the reception and signal processing of the ultrasonic wave are repeated along the depth direction of the subject. as shown in B), the luminance in section S ₂ is obtained bright second image signal. By repeating transmission and reception of ultrasonic waves in this way, finally, transmitting an ultrasonic beam toward the Mth transmission direction, and repeating reception and signal processing of ultrasonic waves along the depth direction of the subject , as shown in (C) of FIG. 4, the image signal of the M luminance is bright in section S _M is obtained.

  The image synthesis unit 38 can obtain one type of image signal with improved contrast by synthesizing the first to Mth image signals. The image compositing unit 38 may add and average a plurality of luminance values respectively represented by the first to Mth image signals, or add these luminance values multiplied by a predetermined coefficient for weighting. Also good. In this manner, speckle pattern components can be reduced by superimposing image signals having different transmission beam intensities in each unit. A speckle pattern is an echo pattern in which bright and dark spots are scattered by wave interference when a group of ultrasonic pulses are added using many structures existing in an organ as an echo source. I mean.

Alternatively, the scan mode conversion unit 35, a waveform signal section S ₁ to S _M to generate respectively the transmission direction of the first to M, the image signal generation unit 36, the section S for the transmission direction of the first to M ₁ to S _M image signal generated each image combining unit 38, by combining the image signals of the first to M representing an image section S ₁ to S _M which constitutes one screen, respectively, one of An image signal may be obtained.

  In the above, an example in which ultrasonic transmission, reception, and signal processing are alternately performed has been described. However, signal processing may be performed after reception of ultrasonic waves is completed in all transmission directions.

  INDUSTRIAL APPLICABILITY The present invention can be used in an ultrasound imaging apparatus that is used to perform diagnosis and non-destructive inspection of an organ in a living body by transmitting and receiving ultrasound and displaying an ultrasound image of a subject. .

1 is a block diagram illustrating a configuration of an ultrasonic imaging apparatus according to an embodiment of the present invention. It is a figure which expands and shows the transducer array shown in FIG. It is a figure which shows the correspondence of the echo waveform and image information in one Embodiment of this invention. It is a figure which shows a response | compatibility with the image signal and the scanning area | region in a subject in one Embodiment of this invention. It is a figure for demonstrating a sector scanning system. It is a figure for demonstrating the interpolation process of image information.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Ultrasonic imaging device main body 11 Transducer array 11a Ultrasonic transducer 20 Switching circuit 21 Transmission circuit 22 Reception circuit 30 Computer 31 Scan control part 32 Waveform data generation part 33 Transmission memory 34 Reception memory 35 Scanning system conversion Unit 36 Image signal generation unit 37 Image memory 38 Image composition unit 39 Image processing unit 40 Recording unit 50 Display unit

Claims (9)

Ultrasound includes a plurality of ultrasonic transducers that form an ultrasonic beam according to a plurality of drive signals, transmit the ultrasonic beam to the subject, and receive an ultrasonic echo reflected from the subject to generate a plurality of received signals, respectively. With a probe,
A plurality of drive signals are sent to the plurality of ultrasonic waves so as to scan a subject over a predetermined scanning range by sequentially transmitting a plurality of ultrasonic beams in a plurality of different transmission directions from the ultrasonic probe. Transmitting means for supplying each to the transducer;
Waveforms of ultrasonic echoes in all pixels included in the scan range of the subject by performing phase matching processing on a plurality of reception signals obtained by the ultrasonic transducers receiving ultrasonic echoes Scanning method conversion means for generating a waveform signal representing information;
Image signal generation means for generating an image signal representing the luminance in all pixels included in the scanning range of the subject based on the waveform signal generated by the scanning method conversion means;
Storage means for storing each of a plurality of types of image signals generated by the image signal generation means for the plurality of different transmission directions;
Image synthesis means for obtaining one type of image signal by synthesizing images represented by a plurality of types of image signals stored in the storage means;
An ultrasonic imaging apparatus comprising:   The ultrasonic imaging apparatus according to claim 1, wherein the scanning method conversion unit converts a received signal obtained by scanning a subject according to a sector scanning method into a waveform signal according to a scanning method used in a display device. Said scanning system conversion means, based on a plurality of receiving signals obtained for one direction of transmission, the generating one type of waveform signals with each of all the pixels included in the scanning range of the subject, according to claim 1 Or the ultrasonic imaging device of 2. The scanning method conversion unit generates waveform signals for all pixels included in the scanning range of the subject without performing interpolation processing on the waveform signals. The ultrasonic imaging apparatus described. The image signal generation means obtains an effective value of the waveform represented by the waveform signal generated by the scanning method conversion means, thereby obtaining an image signal representing the luminance in all pixels included in the scan range of the subject. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic imaging apparatus is generated. The image signal generation unit detects an envelope of a waveform represented by the waveform signal generated by the scanning method conversion unit, thereby obtaining an image signal representing luminance in all pixels included in the scan range of the subject. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic imaging apparatus is generated.   The image synthesizing unit obtains one type of image signal by averaging the plurality of luminance values respectively represented by the plurality of types of image signals stored in the storage unit. The ultrasonic imaging apparatus according to 1.   2. The image synthesizing unit obtains one type of image signal by multiplying a plurality of luminance values respectively represented by the plurality of types of image signals stored in the storage unit by a predetermined coefficient and adding them. The ultrasonic imaging apparatus of any one of -6.   7. The image synthesizing unit according to claim 1, wherein the image synthesizing unit obtains one type of image signal by combining a plurality of types of image signals that are stored in the storage unit and respectively represent images of a plurality of sections constituting one screen. The ultrasonic imaging apparatus of any one of Claims.

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