JP3665406B2 - Ultrasonic diagnostic equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic diagnostic apparatus that transmits ultrasonic waves as burst waves.
[0002]
[Prior art]
The ultrasonic diagnostic apparatus has an advantage that does not exist in other modalities that do not have the problem of exposure like X-rays and that can observe a tomographic image and blood flow information in real time.
By the way, blood flow information is measured based on the frequency shift due to the Doppler effect. Therefore, it is important to narrow the ultrasonic transmission frequency in terms of improving the measurement accuracy of blood flow information. For this reason, in recent years, so-called burst driving in which an ultrasonic pulse having a specific transmission frequency is repeatedly transmitted at a constant period (burst frequency) is sometimes employed.
[0003]
However, since the time width (burst length) of this burst wave is longer than that of a single pulse, the distance resolution is lower than that of a single pulse and the position is shifted. This is due to the fact that reflected waves from various depths corresponding to the burst length are superimposed on the reflected waves that reach the probe at the same timing. Therefore, the depth recognized on the device side is different from the actual depth.
[0004]
By the way, the burst length of the burst wave used in the Doppler mode for obtaining blood flow information is usually significantly longer than the burst length of the burst wave used in the B mode for obtaining a tomographic image. For example, the burst wave number of the burst wave used in the B mode is 2 waves, but the burst wave number of the burst wave used in the Doppler mode is 8 waves or more. Therefore, depending on the difference in burst length between the two modes, the amount of positional deviation differs between the two modes, causing the following problems. In the spectrum Doppler mode, the sample volume is set on the tomographic image. The position of the sample volume is obtained in the coordinate system of the tomographic image. A blood flow velocity distribution is created using blood flow velocity data of pixels corresponding to the obtained position of the sample volume. Therefore, the blood flow velocity distribution at a position different from the sample volume on the tomographic image is provided due to the difference in the positional deviation amount. In the so-called color flow mapping mode in which a two-dimensional distribution (blood flow image) such as blood flow velocity is superimposed on a color tomographic image and displayed in color, the positional relationship between the tomographic image and the blood flow image is shifted. End up.
[0005]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an ultrasonic diagnostic apparatus that solves the problem of misalignment even when burst waves are used.
[0006]
[Means for Solving the Problems]
An ultrasonic diagnostic apparatus according to the present invention includes a scanning unit that scans a cross section of a subject with an ultrasonic burst wave, a unit that generates a tomographic image based on an output of the scanning unit, and an output of the scanning unit In order to pass only the frequency component included in the bandwidth determined by the burst frequency and the number of burst waves of the burst wave, the phase detection means for detecting the Doppler signal from the phase detection means according to the burst length of the burst wave A band-pass filter for filtering with a tap length T, a high-pass filter for removing clutter components from the output of the band-pass filter, means for generating a two-dimensional blood flow image based on the output of the high-pass filter, and the tomography Means for synthesizing and displaying the image and the blood flow image on one screen, and the start timing of the processing of the high-pass filter. Serial comprising a delay means for delaying T / 2 with respect to the output timing from the bandpass filter.
[0009]
According to the present invention, the positional deviation between the tomographic image and the blood flow image is eliminated by a simple process of delaying the start timing of the high-pass filter processing by T / 2 with respect to the output timing from the bandpass filter .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an ultrasonic diagnostic apparatus according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram of the ultrasonic diagnostic apparatus according to the first embodiment. The probe 11 has a piezoelectric vibrator as an acoustic / electric reversible conversion element such as a piezoelectric ceramic. A plurality of piezoelectric vibrators are arranged in parallel and are provided at the tip of the probe 11. A transmission system 13 and a reception system 15 are connected to the probe 11. Although not shown, the transmission system 13 includes a pulse generator, a transmission delay circuit, and a pulse driver. The pulse generator generates a rate pulse at a rate frequency of 5 KHz, for example. This rate pulse is distributed to the number of channels and sent to the transmission delay circuit. The transmission delay circuit provides each rate pulse with a delay time necessary for focusing the ultrasonic wave into a beam and determining transmission directivity. The pulse driver burst-drives the piezoelectric vibrator of the probe 11 for each channel in order to transmit a burst wave from the probe 11 at the timing of receiving the rate pulse from the transmission delay circuit. By this burst driving, an ultrasonic pulse is repeatedly transmitted from the probe 11 n times at a constant period 1 / fb (fb is a burst frequency). Note that n is defined as the burst wave number. Such a group of n ultrasonic pulses is defined as a burst wave.
[0011]
The reflected wave reflected by the discontinuous surface of the acoustic impedance in the subject is received by the probe 11. A reception signal output from the probe 11 for each channel is taken into the reception system 15. Although not shown, the reception system 15 includes a preamplifier, a reception delay circuit, and an adder. The received signal is amplified by a preamplifier for each channel, given a delay time necessary for determining the reception directivity by a reception delay circuit for each channel, and added by an adder. Thereby, the reflection component from the direction according to the reception directivity is emphasized. The overall directivity of ultrasonic transmission / reception is determined by the transmission directivity and the reception directivity. In general, transmission directivity and reception directivity are matched. By repeating such transmission and reception while changing the overall directivity, scanning for one frame is performed.
[0012]
An output signal from the reception system 15 is sent to an envelope detection circuit 17 and a quadrature phase detection circuit 19. The envelope detection circuit 17 detects the envelope of the output signal from the reception system 15. This detection signal is supplied as a video image signal to a monitor 29 via a digital scan converter (DSC) 27, and is visually displayed as a tomographic image (B-mode image) in grayscale.
[0013]
Although not shown, the quadrature detection circuit 19 includes a reference signal generator, a 90 ° phase shifter, two systems of mixers, and two systems of low-pass filters. Output signals from the reception system 15 are respectively taken into two systems of mixers. The reference signal generator generates a reference signal having a fundamental frequency f0 (for example, f0 = 3.5 MHz) of the transmission ultrasonic wave. This reference signal is multiplied with the output signal from the receiving system 15 by one mixer. The reference signal is multiplied with the output signal from the receiving system 15 by the other mixer via a 90 ° phase shifter. The output signals of the two systems of mixers contain harmonic components. This harmonic component is removed by a low-pass filter. As a result, a Doppler signal having only a shifted frequency component subjected to frequency shift due to the Doppler effect is extracted.
[0014]
The range gate integration circuit 21 has both a function as a range gate and a function as an integration circuit. The range gate integration circuit 21 starts integration at a timing corresponding to the first depth with respect to the Doppler signal from the quadrature detection circuit 19, and performs integration at a timing corresponding to a second depth deeper than the first depth. finish. Doppler signals supplied outside the integration period are discarded. Thereby, the Doppler signal only in the range from the first depth to the second depth can be detected as the integration signal. This integration period is controlled by the gate controller 37.
[0015]
The output signal from the range gate integration circuit 21 includes clutter components from organs that move relatively slowly in addition to blood flow components. This clutter component is removed by a high pass filter (HPF) 23. The Doppler signal of only the blood flow component that has passed through the high-pass filter 23 is sent to a fast Fourier transform unit (FFT) 25 as a frequency analysis unit. The fast Fourier transform unit 25 separates a plurality of frequency components included in the Doppler signal including only blood flow components. The output of the fast Fourier transform unit 25 is displayed along the time axis as a spectrum (blood flow velocity distribution) as shown in FIG.
[0016]
A sample volume marker is overlaid on the tomographic image displayed on the monitor 29 as shown in FIG. This overlay data is created by a graphic display controller (GDC) 35 based on the position information of the sample volume from the CPU 31 as the control center of the entire system, and sent to the monitor 29 via the digital scan converter 27. A trackball 33 as an input device is connected to the CPU 31. When the operator appropriately operates the trackball 33, the sample volume marker moves on the tomographic image accordingly.
[0017]
The position information of the sample volume is also sent from the CPU 31 to the gate controller 37. The gate controller 37 controls the integration period of the range gate integration circuit 21 based on this position information.
[0018]
Next, the operation of the present embodiment will be described. The burst length C of the burst wave is defined by the following equation (1).
C = n * (V / fb) * 1/2 (1)
However, n: Burst wave number V: Propagation speed of ultrasonic waves in the living body (sound speed)
fb: Multiplying by 1/2 in the ultrasonic transmission frequency (1) is because the positional shift does not occur in the ultrasonic transmission process and the reception process, but only in the transmission process.
[0019]
Since the positional shift is caused by the difference between the burst length in the B mode and the burst length in the Doppler mode, the burst length C ′ is strictly transformed into the formula (2) in order to eliminate the positional shift. There is a need.
[0020]
C ′ = (nm) × (V / fb) × 1/2 (2)
However, m: Burst wave number of B mode However, practically, n >> m, so even if equation (1) is used, the problem of positional deviation between B mode and Doppler mode is substantially solved. I can.
[0021]
FIG. 2 is a diagram schematically showing signal waveforms relating to rasters on the sample volume. By the operation of the trackball 33 by the operator, the sample volume is set at a desired position on the tomographic image as shown in FIG. The position information of the sample volume is supplied from the CPU 31 to the gate controller 37. The gate controller 37 controls the range gate integration circuit 21 based on this position information, and applies the range gate at a timing according to the depth of the sample volume. The Doppler signal sent from the quadrature detection circuit 19 within a period corresponding to the time width of the range gate is integrated by the range gate integration circuit 21.
[0022]
The gate controller 37 sets the timing for applying the range gate as follows. This timing is measured by the elapsed time starting from the burst wave transmission timing T0. This elapsed time is determined based on the depth of the sample volume. Conventionally, the timing T1 for applying the range gate is set to a timing after an elapsed time corresponding to the depth of the sample volume from the starting point T0.
[0023]
In the present embodiment, the timing T2 for applying the range gate is set with a delay of half the burst length C, that is, C / 2 from the timing T1 corresponding to the depth of the sample volume from the starting point T0.
[0024]
In this way, delaying the timing for applying the range gate by a time of C / 2 from the timing corresponding to the depth of the sample volume means that the range gate is positioned deeper by d / 2 than the distance d corresponding to the burst length. Is equivalent to applying. As described above, in the burst wave, the sensitivity center of the reflected wave is located deeper by d / 2. Therefore, the position shift due to the burst length (time width) of the burst wave is eliminated, and blood flow information regarding a specific depth in which the sample volume is set can be obtained.
(Second Embodiment)
FIG. 4 is a block diagram of an ultrasonic diagnostic apparatus according to the second embodiment. The probe 51 has a piezoelectric vibrator as an acoustic / electric reversible conversion element such as a piezoelectric ceramic. A plurality of piezoelectric vibrators are arranged in parallel and mounted at the tip of the probe 51. A transmission system 53 and a reception system 55 are connected to the probe 51. Although not shown, the transmission system 53 includes a pulse generator, a transmission delay circuit, and a pulse driver. The pulse generator generates a rate pulse at a rate frequency of 5 KHz, for example. This rate pulse is distributed to the number of channels and sent to the transmission delay circuit. The transmission delay circuit provides each rate pulse with a delay time necessary for focusing the ultrasonic wave into a beam and determining transmission directivity. The pulse driver burst-drives the piezoelectric vibrator of the probe 51 for each channel in order to transmit a burst wave from the probe 51 at the timing of receiving the rate pulse from the transmission delay circuit. By this burst driving, an ultrasonic pulse is repeatedly transmitted from the probe 51 n times at a fixed period 1 / fb (fb is a burst frequency). Note that n is defined as the burst wave number. Such a group of n ultrasonic pulses is defined as a burst wave.
[0025]
The reflected wave reflected by the discontinuous surface of the acoustic impedance in the subject is received by the probe 51. The reception signal output from the probe 51 for each channel is taken into the reception system 55. Although not shown, the receiving system 55 includes a preamplifier, a reception delay circuit, and an adder. The received signal is amplified by a preamplifier for each channel, given a delay time necessary for determining the reception directivity by a reception delay circuit for each channel, and added by an adder. Thereby, the reflection component from the direction according to the reception directivity is emphasized. The overall directivity of ultrasonic transmission / reception is determined by the transmission directivity and the reception directivity. In general, transmission directivity and reception directivity are matched. By repeating such transmission and reception while changing the overall directivity, scanning for one frame is performed.
[0026]
An output signal from the reception system 55 is sent to the envelope detection circuit 17 and the quadrature phase detection circuit 59. The envelope detection circuit 17 detects the envelope of the output signal from the reception system 55. This detection signal is supplied as a video image signal to a monitor 73 via a digital scan converter (DSC) 71, and is visually displayed as a tomographic image (B-mode image) in grayscale.
[0027]
Although not shown, the quadrature detection circuit 59 includes a reference signal generator, a 90 ° phase shifter, two systems of mixers, and two systems of low-pass filters. Output signals from the reception system 55 are respectively taken into two mixers. The reference signal generator generates a reference signal having a fundamental frequency f0 (for example, f0 = 3.5 MHz) of the transmission ultrasonic wave. This reference signal is multiplied with the output signal from the receiving system 55 by one mixer. The reference signal is multiplied with the output signal from the receiving system 55 by the other mixer via a 90 ° phase shifter. The output signals of the two systems of mixers contain harmonic components. This harmonic component is removed by a low-pass filter. As a result, a Doppler signal having only a shifted frequency component subjected to frequency shift due to the Doppler effect is extracted.
[0028]
The matched filter 61 is a bandpass filter that allows only frequency components included in the bandwidth determined by the burst frequency and the burst wave number to pass. The specific process is to determine the tap length so that the burst length = tap length. The moving average is performed for the number of taps.
[0029]
The output signal of the matched filter 61 is supplied to the color flow mapping processing system 63. The color flow mapping processing system 63 generates a two-dimensional blood flow image based on the output signal of the matched filter 61. The blood flow image refers to an average velocity image, a dispersion image, a power image, or an appropriate combination image thereof. The color flow mapping processing system 63 includes an MTI filter 65, a frequency analysis unit 67 such as a high-speed autocorrelator, and a calculation unit 69. The MTI filter 65 is configured as a high-speed high-pass filter for removing, in real time, clutter components from a reflector having a slow motion speed such as a myocardium from the output signal (Doppler signal) of the matched filter 61 for each of a large number of sample points. The For one raster, sample points are set at intervals of 0.5 mm, for example. The output of the MTI filter 65 is sent to the frequency analysis unit 67 where the frequency analysis is performed in real time. The analysis result is supplied to the calculation unit 69. Based on the frequency analysis result, the calculation unit 69 calculates the average velocity, the distribution of the velocity distribution, and the power corresponding to the reflection intensity for each sample point. As shown in FIG. 6, the output of the calculation unit 69 is displayed on the monitor 73 as a blood flow image (CFM image) superimposed on the tomographic image in color via the digital scan converter 71.
[0030]
As shown in FIG. 6, the tomographic image displayed on the monitor 73 is overlaid with the ROI marker representing the region of interest for displaying the blood flow image. This overlay data is generated by a graphic display controller (GDC) 79 with respect to a true ROI position signal from the CPU 75 as a control center of the entire system, and is sent to the monitor 73 via the digital scan converter 71. A trackball 77 as an input device is connected to the CPU 75, and when the operator appropriately operates the trackball 77, the position and range of the ROI marker are changed accordingly.
[0031]
The MTI controller 81 controls the processing start timing of the color flow mapping processing system 63 based on the tap length of the matched filter 61 with respect to the output timing of the matched filter 61.
[0032]
Next, the operation of the present embodiment will be described. For the burst length C of the burst wave, refer to the first embodiment.
By operating the trackball 77 by the operator, the ROI is set at a desired position and range on the tomographic image as shown in FIG. The ROI position and range information is supplied from the CPU 75 to the MTI controller 81.
[0033]
FIG. 5 is a diagram illustrating the timing of the operation control signal supplied from the MTI controller 81 to the MTI filter 65 with respect to the output signal of the matched filter 61 for a certain raster in the ROI. The MTI controller 81 supplies an operation control signal to the MTI filter 65. The MTI filter 65 performs the filter operation while receiving the operation control signal. The frequency analysis unit 67 and the calculation unit 69 operate in response to the output from the MTI filter 65. Therefore, the processing start timing of the color flow mapping processing system 63 is determined depending on the operation start timing of the MTI filter 65.
[0034]
The matched filter 61 filters and passes only the Doppler signal corresponding to the ROI under the control of the CPU 75, and discards the other Doppler signals.
The MTI controller 81 controls the start timing of supplying the operation control signal to the MTI filter 65 to set the timing at which the CFM processing is substantially started as follows. Conventionally, this timing is synchronized with the timing at which the output signal from the matched filter 61 is supplied to the MTI filter 65. In the present embodiment, this timing is delayed with respect to the timing at which the output signal from the matched filter 61 is supplied to the MTI filter 65 by a half of the tap length T of the matched filter 61, that is, a time of T / 2. . The tap length T is determined according to the burst length as described above.
[0035]
After the matched filter 61, the position of the first output of the matched filter 61 is recognized as the shallowest part of the ROI. According to the matched filter processing that is indispensable when a burst wave is used, the signal corresponding to the shallowest portion of the ROI is located at a position delayed by a time of T / 2 after the operation of the matched filter 61 is started. Therefore, as described above, the timing T1 ′ at which the CFM processing is started is the time T / 2 from the timing T1 at which the output signal from the matched filter 61 is started to be supplied to the CFM processing system 63, specifically, the MTI filter 65. By delaying, the positional deviation between the tomographic image and the blood flow image due to the matched filter processing indispensable when the burst wave is used is eliminated.
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.
[0036]
【The invention's effect】
According to the present invention, the positional deviation between the tomographic image and the blood flow image is eliminated by a simple process of delaying the start timing of the high-pass filter processing by T / 2 with respect to the output timing from the bandpass filter.
[0037]
According to the invention of claim 2, the start timing of the generation process of the blood flow image generation means is not synchronized with the output timing from the filter means, but is delayed by T / 2. Thereby, the positional deviation between the tomographic image and the blood flow image corresponding to the tap length of the filter means is eliminated.
[Brief description of the drawings]
FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to a first embodiment.
FIG. 2 is a diagram showing timing for applying a range gate according to the first embodiment.
FIG. 3 is a diagram showing an example of a monitor display screen.
FIG. 4 is a block diagram of an ultrasonic diagnostic apparatus according to a second embodiment.
FIG. 5 is a diagram showing an operation start timing of the MTI filter according to the second embodiment.
FIG. 6 is a diagram showing an example of a monitor display screen.
[Explanation of symbols]
11 ... probe, 13 ... transmission system,
15 ... Reception system, 17 ... Envelope detection circuit,
19 ... Quadrature detection circuit, 21 ... Range gate integration circuit,
23: high-pass filter, 25 ... fast Fourier transform,
27: Digital scan converter, 29 ... Monitor,
31 ... CPU, 33 ... trackball,
35 ... Graphic display controller,
37 ... Gate controller.

Claims (1)

Scanning means for scanning the cross section of the subject with an ultrasonic burst wave;
Means for generating a tomogram based on the output of the scanning means;
Phase detection means for phase detection of the output of the scanning means;
In order to pass only frequency components included in the bandwidth determined by the burst frequency and the number of burst waves of the burst wave, the Doppler signal from the phase detection means is filtered with a tap length T corresponding to the burst length of the burst wave. A bandpass filter,
A high-pass filter for removing clutter components from the output of the bandpass filter;
Means for generating a two-dimensional blood flow image based on the output of the high-pass filter;
Means for combining and displaying the tomographic image and the blood flow image on one screen;
The ultrasonic diagnostic apparatus of characterized by comprising a delay means for delaying T / 2 relative to the output timing of the band filter or we start timing of the processing of the high-pass filter.

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