JP2007007045A - Ultrasonograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an estimation of a biological sound velocity with an ultrasonograph. <P>SOLUTION: The ultrasonograph comprises an ultrasound probe 1 having a plurality of arranged probes, transmitting circuit 2 to transmit ultrasound waves to a subject via the ultrasound probe 1, a receiving circuit 7 to receive echo signals from the subject via the ultrasound probe 1, and an intensity distribution generating section 15 to generate a plurality of ultrasound intensity distributions with different predetermined sound velocities for delayed control based on received echo signals. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasound diagnostic apparatus that scans the inside of a subject with ultrasound and obtains and displays an ultrasound image based on an obtained echo signal.

  In the ultrasonic diagnostic apparatus, in order to increase the azimuth resolution of an image, a method of focusing transmission and reception beams is employed. In particular, an electronic focusing method based on delay time control of transmission / reception signals of each channel is used in an electronic scanning type array transducer.

The problem with the electron focusing method is that the beam diffuses at a location (depth) away from the focusing point, and the azimuth resolution is lowered. For this purpose, a dynamic focusing method is conventionally used. This is a method of performing delay time control so that the focal point continuously moves in the depth direction with time at the time of reception, and can thereby always be obtained from the focused region of the received ultrasonic beam. At this time, the coordinate in the depth direction of the focal point P as shown in FIG. If the delay time from when the wavefront reaches the center of the aperture until it reaches the above element is Δt, and the sound speed of the medium is C, the following equation (1) is obtained.
Δt = ((X ² + Y ² ) ^1/2 −X) / C (1)
In a general ultrasonic diagnostic apparatus, the sound speed C is set with a delay time assuming a typical sound speed of a target diagnostic site (hereinafter referred to as a set sound speed). However, there are reports that the in-vivo sound velocity value is 1560 cm / s for muscles and 1480 cm / s for fats, and there is a considerable difference between subjects, and the focal point does not match due to this difference in sound velocity, resulting in image quality degradation. There was a problem.

As shown in comparison with FIGS. 9A and 9B, when the set sound speed does not match the actual sound speed in the living body, the focusing point is shifted. Therefore, as a method for detecting the sound speed, there are techniques such as phase correction by a reflection method and a cross-correlation method. However, these have the problem that a reflector such as a calculus or a boundary wall must be present, and that the reflector must be a point, and thus it is difficult to obtain a good image as a whole. Further, Patent Document 1 describes a technique that allows the sound speed to be arbitrarily changed, but the sound speed itself cannot be measured.
JP-A-8-317926

  An object of the present invention is to realize estimation of a living body sound speed in an ultrasonic diagnostic apparatus.

  In an aspect of the present invention, an ultrasonic diagnostic apparatus includes an ultrasonic probe having a plurality of arranged transducers, a transmission circuit that transmits ultrasonic waves to a subject via the ultrasonic probe, A receiving circuit that receives an echo signal from the subject via an ultrasonic probe and a plurality of ultrasonic intensity distributions having different set sound speeds for delay control based on the received echo signal An intensity distribution generation unit.

  According to the present invention, it is possible to estimate the biological sound speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of an ultrasonic diagnostic apparatus according to this embodiment. The ultrasonic probe 1 has a plurality of arranged piezoelectric elements. The form of the ultrasonic probe 1 is arbitrarily selected from sector correspondence, linear correspondence, convex correspondence, and the like. A transmission circuit 2 for transmitting an ultrasonic wave from the ultrasonic probe 1 includes a clock generator 3, a rate pulse generator 4, a transmission delay circuit 5, and a pulser 6. A rate pulse for determining an ultrasonic transmission rate (number of transmissions per second) is output from the rate pulse generator 4 in accordance with the clock oscillated from the clock generator 3. This rate pulse is delayed by the transmission delay circuit 5. Under the control of the scan controller 13, the delay time is set for each transducer in order to focus the ultrasonic wave. The pulser 6 is triggered by the delayed rate pulse and applies a high-frequency pulse voltage to the transducer of the probe 1. The transducer of the probe 1 receives this pulse voltage and vibrates mechanically. Thereby, an ultrasonic wave is generated and transmitted to the subject.

  Ultrasound propagates in the living body and is reflected one after another at a discontinuous surface of acoustic impedance in the middle. This reflection intensity mainly depends on the difference in acoustic impedance of the discontinuous surface. The echo due to such reflection returns to the probe 1 and vibrates the vibrator. As a result, a weak electric signal is generated from the vibrator. This electric signal is taken into the receiving circuit 7. The receiving circuit 7 includes an analog-digital converter (ADC) 8, typically a random access memory (RAM) 9 as a storage unit, and a digital adder 10. The analog-digital converter 8 is provided for each transducer or each channel, and converts an electrical signal from the corresponding probe 1 into a digital signal. Similar to the analog-digital converter 8, the random access memory 9 is provided for each transducer or channel, and holds a digital signal (echo signal). The digital adder 10 adds (phased addition) echo signals read from the random access memory 9 under the control of the scan controller 13. The scan controller 13 controls the timing of reading the echo signal from the random access memory 9, thereby determining the ultrasound focusing and the focusing depth (focus depth). Specifically, the readout timing is a time difference (delay time) between the signal readout time of the open end channel and the signal readout time of another channel read later. The depth of focus can be changed by controlling the delay time applied to each channel. In addition, the aperture width and the center of the aperture can be controlled by limiting the channels from which signals are read almost simultaneously. The display 11 displays an ultrasonic image based on the added signal.

  In the present embodiment, a beam profile generation unit 15 and a sound speed selection unit 16 are characteristically provided. The beam profile generation unit 15 displays a plurality of generated beam profiles on the same screen together with a function of generating a plurality of beam profiles having different set sound speeds from the echo signal subjected to phasing addition by the receiving circuit 7. The function of generating a signal for The sound speed assumed for setting the delay time is referred to as a set sound speed. The beam profile is an intensity distribution with respect to the azimuth direction of the ultrasonic intensity. The sound speed selection unit 16 estimates the biological sound speed from a plurality of beam profiles having different set sound speeds. Specifically, the set sound speed of the beam profile corresponding to the minimum beam width among the plurality of beam profiles is selected as the biological sound speed.

  FIG. 2 shows the procedure of the biological sound speed measurement operation according to this embodiment. FIG. 3 is a supplementary diagram of FIG. Here, a linear scan will be described as an example, but the biological sound speed measurement operation can be applied to other scanning methods such as a sector. The biological sound speed measurement operation is started under the control of the system controller 14 in accordance with the operation start instruction of the operator input from an input device (not shown). Alternatively, the biological sound speed measurement operation may be automatically performed periodically by the system controller 14 during the ultrasonic examination. In the biological sound velocity measurement operation, first, the transmission circuit 2 controlled by the scan controller 13 drives the ultrasonic probe 1 to transmit ultrasonic waves to the subject (S11). As illustrated in FIG. 3, ultrasonic waves are generated from a plurality of transducers in an opening having a predetermined width centered on a predetermined opening center YT under the control of the scan controller 13. The delay time for each transducer is determined by the scan controller 13 so that the ultrasonic waves are focused at a focal point T of a predetermined depth under a standard sound velocity C0 in water (for example, 1524 m / sec). Is done. The transmission delay circuit 5 sets a delay time determined for each corresponding transducer from the scan controller 13.

  Following the transmission, echoes from the subject are received by all transducers (S12). Actually, echoes (echo signals) converted into electric signals by all transducers are individually converted into digital signals by the analog-digital converter 8 and stored in the corresponding random access memories 9 respectively.

  The echo signal stored in the random access memory 9 is read under the control of the scan controller 13 (S13), added by the digital adder 10, and a signal phased by the addition (to distinguish it from the echo signal). (Referred to as a received signal) is stored in the received signal storage unit 11 (S14). Reading (S13) and addition and storage (S14) are controlled by the system controller 14, and the variables j, i, and k reach n, N, and k, respectively, through the determination processes of S15, S16, and S17. Repeat until. The variable i corresponds to the change in the set sound velocity Ci, j corresponds to the change in the reception aperture center position (position in the azimuth direction), and k corresponds to the change in the focal depth Pk. In the linear scanning method, the receiving aperture width is typically fixed at a predetermined width (a predetermined predetermined number of transducers m). Variables j, i, and k are initialized to 0, 1, and 1, respectively.

  First, the delay time of each of a predetermined number of transducers centered on the aperture center Y0 is calculated by the scan controller 13 according to the above equation (1) so that the ultrasonic wave is focused on the focal point P1 assuming the set sound velocity C1. According to the calculated delay time, m echo signals in the vicinity are read from the RAM 9, added, and the received signal is stored. Subsequently, through S15, the variable j is incremented by 1, that is, the reception aperture center is shifted to Y1, and m echo signals in the vicinity are read out and added with the same delay time. Is memorized. Reading, adding and storing are repeated until the receiving aperture center position Yj reaches Yn. As a result, reception signals whose reception delay is controlled so as to be focused on the focal point P1 under the assumption of the set sound velocity C1 are individually generated at (n + 1) positions of the aperture centers Y0 to Yn.

  Next, the reception aperture center position Yj is initialized to Y0, the set sound speed is changed to C2, and the ultrasonic wave is received from the RAM 9 according to the delay time calculated so as to be focused on the focal point P1 under the set sound speed C2. M echo signals in the vicinity of the opening center position Y0 are read out, added, and the received signal is stored. Similarly, reading, addition and storage are repeated until the reception aperture center position Yj reaches Yn, whereby the reception signal whose reception delay is controlled so as to converge at the focal point P1 under the assumption of the set sound speed C2. Are generated individually for (n + 1) positions of the opening centers Y0 to Yn.

  In this way, S13, S14 and S15 are repeated until the set sound speed Ci reaches Cn. As a result, a set of (n + 1) received signals having the same depth of focus P1 and the receiving aperture center Yj shifted by a predetermined interval is generated for each of the N set sound velocities Ci, that is, N sets are generated. .

  Similarly, through S17, this time, the depth of focus is changed to P2, the depth of focus is the same at P2, and the set of (n + 1) received signals in which the reception aperture center Yj is shifted by a predetermined interval is It is generated for each of N kinds of set sound speeds Ci, that is, N sets are generated.

  Next, the beam profile generation unit 15 generates a beam profile representing the spatial distribution of the ultrasonic intensity (power) in the azimuth direction as illustrated in FIG. 4 for each set, that is, for each set sound speed (S18). As shown in FIG. 4, 10 types of beam profiles are generated corresponding to the depth of focus P1, with n = 9 and the set sound speed from 1440 m / sec to 1620 m / sec. Signals for displaying 10 types of beam profiles having different set sound velocities corresponding to the focal depth P1 (shallow region) are generated by the beam profile generation unit 15 and supplied to the display 12. The display unit 12 displays ten types of beam profiles superimposed as shown in FIG. Similarly, ten types of beam profiles corresponding to the focal depth P2 (deep region) are generated and displayed.

  The sound speed selection unit 16 selects, for example, a beam profile having the narrowest half width (shortest) as a beam width from ten types of beam profiles having different set sound speeds corresponding to the focal depth P1 (shallow region). The set sound velocity Ci corresponding to the beam profile thus obtained is estimated as the biological velocity related to the shallow region of the part of the subject (S19). That is, the set sound speed when the beam width is narrowed down most closely approximates the true biological speed. Similarly, the sound speed selection unit 16 selects, for example, a beam profile having the narrowest half width as a beam width from ten types of beam profiles having different set sound speeds corresponding to the focal depth P2 (deep region). The set sound velocity Ci corresponding to the beam profile is estimated as the biological velocity related to the deep region of the part of the subject (S19).

  Data on the biological velocity estimated for each shallow region and deep region is supplied to the scan controller 13 (S20). The scan controller 13 controls transmission and reception delay times according to the estimated biological speed.

  Thereby, the set sound speed used for the delay control can be automatically set to a value that is the same as or close to the actual medium sound speed, a high-resolution high-quality image can be obtained, and the diagnostic accuracy can be further improved.

  In the above description, the beam profile generation unit 15 generates a plurality of beam profiles having different set sound speeds as illustrated in FIG. 4, but generates a graph representing changes in the beam width depending on the set sound speeds as illustrated in FIG. At the same time, the change may be approximated by a quadratic curve, typically as a multi-order curve. Further, the beam profile generator 15 generates a signal for displaying the generated graph together with the approximate curve in the beam profile generator 15 and supplies the signal to the display 12.

  In the above description, the sound speed selection unit 16 selects a beam profile having the minimum beam width from a plurality of beam profiles and estimates the set sound speed corresponding to the selected beam profile as the biological speed. The person may manually select from a plurality of beam profiles displayed on the display device 12 based on his / her own judgment through an input device (not shown).

  In the above description, the sound speed selection unit 16 selects the beam profile having the minimum beam width from the plurality of beam profiles, and estimates the set sound speed corresponding to the selected beam profile as the biological speed, as shown in FIG. Alternatively, the minimum value of the approximate curve may be extracted, and the set sound speed corresponding to the minimum value may be estimated as the biological speed.

  Further, the beam profile generation unit 15 may generate the image 20 illustrated in FIG. The image 20 generates partial images 20-1 to 20-N for each set sound speed by arranging (n + 1) reception signals having the same depth of focus along the azimuth axis, and the difference in the set sound speeds. The N partial images 20-1 to 20-N to be generated are arranged in order of sound speed. The beam profile generation unit 15 generates a signal for displaying the image 20. In accordance with this signal, the image shown in FIG.

  From the displayed image 20, any partial image 20-1 to 20 -N is manually selected by the operator through his / her own determination via an input device (not shown), and a set sound speed corresponding to the partial image is set. May be estimated as the biological velocity.

  In the above description, the ultrasonic wave is transmitted only once at the position YT. However, the ultrasonic wave may be repeatedly transmitted from a plurality of positions around the position YT. At that time, a plurality of echo signals with different transmission positions, the same center of reception aperture and the same focal depth are averaged (averaged), and the received signals are generated by phasing and adding the averaged echo signals. A beam profile may be generated from the signal. FIG. 7 shows an image 21 similar to that shown in FIG. 6 using a reception signal generated from the averaged echo signal. In this case, the SNR is clearly improved.

  Furthermore, in the above description, (n + 1) received signals having different receiving aperture centers Yj are generated for each shallow / deep region from the stored echo signal by the digital beam forming technique. However, like the conventional analog beam forming, A single reception signal is generated for each ultrasonic transmission and is repeated as many times as necessary. That is, the ultrasonic transmission is repeated, and the reception aperture center Yj is shifted each time reception is performed. .

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a diagram showing a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. The figure which shows the procedure of the biological sound speed measurement operation | movement in this embodiment. FIG. 3 is a supplementary diagram of S1 and S13 of FIG. The figure which shows the example of a display of the beam profile produced | generated by the beam profile production | generation part of FIG. The figure which shows the example of a display of the relationship between the beam width produced | generated by the beam profile production | generation part of FIG. 1, and setting sound speed. The figure which shows the example of a display of the synthesized image of the intensity image for every setting sound speed produced | generated by the beam profile production | generation part of FIG. The figure which shows the example of a display of the synthesized image of the average intensity image for every setting sound speed produced | generated by the beam profile production | generation part of FIG. FIG. 6 is a supplementary diagram for calculating the delay time Δt for ultrasonic focusing. The figure which shows the shift | offset | difference of the focus by the mismatch with the setting sound speed for delay control, and an actual biological sound speed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic probe, 2 ... Transmission circuit, 3 ... Clock generator, 4 ... Rate pulse generator, 5 ... Transmission delay circuit, 6 ... Pulser, 7 ... Reception circuit, 8 ... Analog-digital converter (ADC) , 9 ... Random access memory (RAM), 10 ... Digital adder, 11 ... Received signal storage unit, 12 ... Display, 13 ... Scan controller, 14 ... System controller, 15 ... Beam profile generation unit, 16 ... Sound speed selection unit .

Claims (10)

An ultrasonic probe having a plurality of arranged transducers;
A transmission circuit that transmits ultrasonic waves to the subject via the ultrasonic probe;
A receiving circuit for receiving an echo signal from the subject via the ultrasonic probe;
An ultrasonic diagnostic apparatus comprising: an intensity distribution generation unit that generates a plurality of ultrasonic intensity distributions having different set sound speeds for delay control based on the received echo signal. The ultrasonic diagnostic apparatus according to claim 1, further comprising an estimation unit configured to estimate a biological sound speed of the subject based on the plurality of ultrasonic intensity distributions. The ultrasonic diagnostic apparatus according to claim 2, wherein the estimation unit estimates a set sound speed of an ultrasonic intensity distribution corresponding to a minimum beam width among the plurality of ultrasonic intensity distributions as the biological sound speed. The ultrasonic diagnostic apparatus according to claim 2, further comprising a control unit that controls the transmission circuit and the reception circuit so that delay control is performed according to the estimated biological sound velocity. The ultrasonic diagnostic apparatus according to claim 2, wherein the estimation unit estimates the biological sound velocity individually for a plurality of depth regions. The ultrasonic diagnostic apparatus according to claim 1, further comprising a display signal generation unit that generates a signal for displaying the plurality of ultrasonic intensity distributions on the same screen. 2. The super of claim 1, further comprising an average adder that averages and adds a plurality of echo signals having different transmission aperture center positions of the ultrasonic waves and substantially the same reception aperture center positions of the echo signals. Ultrasonic diagnostic equipment. A method in which the control means controls each part of the ultrasonic diagnostic apparatus,
Controlling the transmission circuit to repeatedly generate ultrasonic waves;
Controlling the receiving circuit to repeatedly receive an echo signal;
Generating a plurality of ultrasonic intensity distributions having different set sound speeds for delay control based on the received echo signals;
And a step of estimating a biological sound velocity of the subject based on the plurality of ultrasonic intensity distributions. Means for generating a plurality of ultrasonic intensity distributions having different set sound speeds for delay control based on echo signals obtained by repetition of ultrasonic transmission and reception;
A computer-readable storage medium storing a program for causing a computer to realize means for estimating the biological sound velocity of the subject based on the plurality of ultrasonic intensity distributions. Means for generating a plurality of ultrasonic intensity distributions having different set sound speeds for delay control based on echo signals obtained by repetition of ultrasonic transmission and reception;
A program for causing a computer to realize means for estimating the biological sound velocity of the subject based on the plurality of ultrasonic intensity distributions.

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