JPH04220243A - Ultrasonic diagnostic device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus using continuous wave Doppler method. In the field of medical diagnosis, ultrasound is used to visualize in-vivo information such as blood flow velocity and use it for diagnosis. Ultrasonic diagnosis involves transmitting continuous ultrasound waves or pulsed ultrasound waves to the subject, receiving echoes from the subject, and analyzing the frequency of the Doppler component in the specific depth echo signal to obtain in-vivo information. It is output as an image. In the pulsed ultrasound method, the position of the reflection point can be estimated based on the round trip time of the echo signal, so spatial resolution can be obtained, but the maximum detected flow velocity is limited by the sampling theorem and is lower than the continuous wave Doppler method. .

On the other hand, the continuous wave Doppler method has a problem in that although the maximum detected flow velocity is high, it does not have sufficient spatial resolution. An object of the present invention is to provide the continuous wave Doppler method with spatial resolution for distinguishing, for example, the relative positions of carotid arteries in the human body when they are known.

0003

2. Description of the Related Art FIG. 9 shows a conventional continuous wave Doppler ultrasonic diagnostic apparatus. Figure (a) shows the configuration of a continuous wave Doppler ultrasonic diagnostic device. In the figure, 81 is an ultrasound probe, 82 is a continuous wave Doppler unit, which outputs the transmitted continuous ultrasound to the ultrasound probe, inputs the echo signal from the subject received by the probe, The Doppler component in the echo signal is sampled, and the time-series signal of the Doppler component is Fourier transformed to create a frequency spectrum.

Reference numeral 84 is a digital scan converter which converts the coordinates of a Doppler spectrum signal for image display. Reference numeral 85 is a display device (CRT). Figure (b
) shows the configuration of the continuous wave Doppler section. In the figure,
Reference numeral 86 is a transmission drive circuit, which drives and outputs the ultrasonic wave to be transmitted to the ultrasonic probe. Reference numeral 87 is an transmitter circuit (OSC), which converts the ultrasonic wave to be transmitted (transmission frequency fc) into an electrical signal. 88 is a receiving drive circuit that drives the received wave (echo signal). 89 is a mixer circuit (MIXER), which inputs the transmission output of the transmission circuit 87 and the received wave driven by the reception drive circuit 88, and calculates the Doppler shift component of the difference between the transmitted wave and the received wave; 89 is a mixer circuit , the transmitting circuit 8
A circuit that outputs the transmission output of 7 and the received wave driven by the reception drive circuit 88 and calculates the Doppler shift component of the difference between the speed and the received wave. 90 is a band filter (B.P.F.) Only the components are extracted. 91
is a fast Fourier transform circuit (FFT) that samples the Doppler shift component at a sampling frequency fs and determines the intensity of the spectrum of the Doppler shift component based on the time series signal obtained by sampling.

The operation of a conventional ultrasonic diagnostic apparatus using the continuous wave Doppler method is as follows. The subject is a living body,
An example in which the moving fluid is blood flow will be explained. The transmission output of the transmission circuit 87 is driven by the transmission drive circuit 86 and transmitted from the ultrasound probe 81 to a subject (not shown). When the transmitted wave is reflected in the blood vessel, it undergoes a Doppler shift according to the moving speed of the blood flow, and is received by the ultrasound probe 81 and becomes a received wave, and the continuous wave Doppler unit 8
2 is input.

If the frequency of the transmitted wave is fc, the Doppler shift component is fd, and the frequency of the received wave subjected to Doppler shift is f, then f=fc±fd (When the blood flow approaches the ultrasound probe 81 +, Ultrasonic probe 81
When it moves away from , it becomes -). The received wave is driven by a reception drive circuit 88 and input to a mixer circuit 89 . The mixer circuit 89 calculates the difference between the transmitting frequency and the receiving frequency based on the transmitting output of the transmitting circuit 87 and the output of the receiving drive circuit 88, inputs the difference between the transmitting frequency and the receiving frequency, and inputs the difference to the band filter 90. Output only the shift component. Fast Fourier transform circuit FFT (sampling circuit) 9
1 samples the Doppler shift component at the sampling frequency fs, creates a time series signal, and obtains the spectrum of the Doppler shift component by fast Fourier transforming the time series signal. The signal is then input to the display device 85 via the digital scan converter 84.

[0007]

[Problems to be Solved by the Invention] In the conventional continuous wave Doppler method described above, the maximum detection velocity of blood flow etc. is high, but it cannot provide spatial resolution and it is difficult to detect blood flow in blood vessels at different depths. It was not possible to distinguish and display the flow. An object of the present invention is to distinguish blood flows at different depths and display them on a screen so that the positional relationship in the depth direction and blood flow velocity can be seen in the continuous wave Doppler method.

[0008]

[Means for Solving the Problems] In continuous wave Doppler ultrasonic diagnosis, the relationship between the Doppler spectrum signal intensity of the reflected wave at a specific position within the subject and the depth of the reflection point is determined by the transmitted ultrasonic wave. By taking advantage of the difference depending on the frequency, we were able to see changes in blood flow for different blood vessels with known depth positions.

Before explaining the basic configuration of the present invention shown in FIG. 1, the principle of the present invention will be explained with reference to FIGS. 2 and 3. Figure 2
FIG. 2 shows an explanatory diagram of the principle of determining the spatial distribution of measurement positions in the present invention. Figure (a) shows the relationship between incident waves and reflected waves on the subject. In the figure, 21 is an ultrasonic probe, 2
2 is a subject, and 23 and 24 are blood vessels 1 and 2, respectively, whose blood flow velocities are v1 and v2, respectively. 25 is a transmitting wave, which irradiates different frequencies fA and fB in the same direction. 26 and 27 are Doppler shift components fd1 and fd2 in blood vessel 1 (23) and blood vessel 2 (24), respectively. Point q is a point located at a depth between blood vessel 1 (23) and blood vessel 2 (24). Figure 2(b)
) indicates the relationship between Doppler spectrum signal strength and depth position (distance in the depth direction). The vertical axis is the Doppler spectrum signal intensity, and the horizontal axis is the distance l in the depth direction. fA, fB
are the frequencies of the transmitted ultrasonic waves, and fB > f
It is A. As shown in the figure, the Doppler spectrum signal intensity at a specific reflection point in the subject for two different transmission frequencies decreases as the distance in the depth direction increases, and the rate of decrease increases as the frequency increases.

The received intensity of the Doppler component is determined by its transmitting ultrasonic frequency f [MHz], attenuation constant α [Neper/MHz]
/cm], and the depth of the reflection point is l [cm], then f4
It is attenuated in proportion to exp(-4αfl). Therefore,
To compare the intensity of blood flow velocity at points P1 and P2,
Consider a case where the intensity of the Doppler spectrum signal in the received signal due to the transmitted ultrasound frequency fA is shifted by Δ as shown in the figure.

[0011] If the attenuation coefficient of the region where the ultrasonic wave propagates is known, it is possible to determine the intersection point P in FIG. 2(b) at a specific depth position. For example, point q in figure (a)
The intersection point P in Figure (b) can be determined so that By doing this, the ratio of the Doppler spectrum signal intensity for different transmitted ultrasound frequencies will be different values when calculating at a shallower depth than point P and when calculating at a deeper point, so the point in Figure (a) If Δ is determined so that point P in Figure (b) corresponds to the position q, blood flow in blood vessel 1 and blood vessel 2 can be distinguished and recognized.

FIG. 3 is an explanatory diagram of the principle of depth position determination, in which the ratio of the intensity of Doppler spectrum signals to transmitted waves of different frequencies is compared at different distances in the depth direction. Figure (a) shows the relationship between the Doppler spectrum signal intensity and the distance in the depth direction for the shifted frequencies fA and fB shown in Figure 2. Point P1,
P2 and P correspond to the positions of blood vessel 1, blood vessel 2, and point q in FIG. 2(a), respectively.

PA1 and PA2 in Figure (b) indicate the intensity of the Doppler spectrum signal with respect to the frequency fA at points P1 and P2. In figure (c), PB
1 and PB2 indicate the intensity of the Doppler spectrum signal with respect to the frequency fB at points P1 and P2. Figure (d)
represents the intensity ratio of Doppler spectrum signals at point P1 and point P2 (ratio of Doppler spectrum signal intensities for different frequencies). Therefore, depending on whether the Doppler spectrum signal strength ratios PA1/PA2 and PB1/PB2 are smaller or larger than 1, it is possible to determine whether points P1 and P2 are located shallower or deeper than position q. .

When the intensity ratio of this Doppler spectrum signal is larger than 1, the color is blueish, and when the ratio is smaller than 1, it is redish. It becomes possible to display the velocity and the blood flow velocity in the blood vessel 2 separately on the screen. In addition, when calculating the ratio of Doppler spectrum signal intensities, in the above description, one of the intensities is shifted by Δ and compared, but it is also possible to compare without shifting. In the following explanation,
The case of shifting will be explained as an example.

FIG. 1 shows the basic configuration of the present invention. In the figure, 1 is an ultrasound probe, 2 is a subject such as a living body, 3,
Reference numeral 4 denotes objects to be measured for moving speed, each of which is a blood vessel as an example. The blood velocity is v1 and v, respectively.
2. 5 and 5' are continuous wave Doppler units, which transmit waves at different frequencies fA and fB, respectively. Reference numeral 7 denotes a signal synthesis unit, which is a ratio of the Doppler spectrum signal intensities generated by reflection at the same depth among the Doppler spectrum signal intensities output from each continuous wave Doppler unit 5, 5' (reflection at position P1 in the figure). The ratio of the intensity of the Doppler spectrum signal of the same speed during reception to the transmitted waves fA and fB caused by the transmission waves fA and fB caused by the reflection at position P2.
The ratio of the intensity k of the Doppler spectrum signal of the same speed being received to that of the Doppler spectrum signal is determined, and the color indicating each position is determined according to the value of the ratio.

100 and 100' are means for transmitting ultrasonic continuous waves. 101 and 101' are means for outputting Doppler spectrum signals. 8 is a transmission drive circuit, 9
1 is a transmitting circuit, 10 is a reception drive circuit, 11 is a Doppler shift component extraction circuit, which is composed of a mixer circuit and a band filter, and extracts the Doppler frequency component of the received wave, and 12 is a sampling circuit. Reference numeral 13 denotes an intensity ratio calculation unit, which calculates, for example, the transmitted waves fA and fB at point P1.
The strength PA of the Doppler spectrum signal during reception for
, PB, the ratio of PA and PB is calculated.

Reference numeral 14 denotes a hue conversion section, which converts the measurement points (P1, P2) based on the calculation result of the intensity ratio calculation section 13.
The color to be displayed on the screen is determined in association with the color. The above processing is performed every time on time-series Doppler echo signal data by extracting Doppler shift components at regular time intervals using a window function at regular time intervals. 1
Reference numeral 5 denotes a display control section, which is made up of a digital scan converter or the like and extracts the signal created in the signal synthesis section 7 and causes it to be displayed on a display device. Reference numeral 16 denotes a display device which displays temporal changes in detected blood velocity at different depths, etc., in a sonogram with time on the horizontal axis, blood velocity on the vertical axis, and the relationship with depth using color and brightness. .

Reference numeral 17 is a Δ adjustment unit which shifts the level of the velocity signal of an arbitrary reflected wave when calculating the intensity ratio of the Doppler spectrum signal. In the figure,
Although the Δ adjustment section 17 is configured to level shift the output of the intensity ratio calculation section 13, it may be provided after the continuous wave Doppler section 5, 5' takes in the received signal. Note that the continuous wave Doppler units 5, 5' are similar to those in the prior art.

[Operation] The operation of FIG. 1 will be explained. The operations of the continuous wave Doppler units 5, 5' are the same as those in the conventional example, so the explanation will be omitted. In the present invention, the sampling frequency may be the same or different between the continuous wave Doppler sections 5 and 5'. The outputs of the continuous wave Doppler sections 5, 5' are input to the intensity ratio calculation section in the signal synthesis section 7. Then, the ratio of the strength of the Doppler spectrum signal to the frequency fA and the strength of the Doppler spectrum signal to the frequency fB at each point P1, P2 is determined.

The hue conversion unit 14 has a table that associates the intensity ratio with the hue described above, and determines the color for the blood flow velocity display at the points P1 and P2 based on the calculation result of the intensity ratio calculation unit 13. The display control section 15 is a display control section composed of a digital scan converter, etc., and takes out the data from the signal synthesis section 7 and displays it in blue for the point P1, for example, and in blue for the point P2. will be displayed on the display device, such as in red. Then, the above process is performed as time passes, the vertical axis is the blood flow velocity, the horizontal axis is time, and the point P
The relationship between 1 and P2 is represented by color and displayed as a sonogram on the screen. .

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. 4 to 8. In the present invention, there are cases where sampling is performed at a sampling frequency where the Doppler shift components in each reflected wave obtained by using different transmission frequencies are equal, and a case where sampling is performed at a sampling frequency where the ratio of the ultrasound frequency and the sampling frequency is constant. There are two methods available for sampling. In the former case, the maximum detected flow velocity differs depending on the ultrasound frequency, whereas in the latter case, the maximum detected flow velocity is the same, but the window function in Fourier transform differs depending on the ultrasound frequency.

FIG. 4 shows the relationship between sampling frequency and maximum detection speed. Figure (a) shows the case where the sampling frequency is constant. Transmission frequency f, sampling frequency fs
The maximum detection speed for VMAX is VMAX = C・fs/4f...(1)
However, C is the speed of sound inside the subject. Therefore, the maximum detection speed for the frequency fA of the transmitted wave is VMAX
A, sampling frequency fs, frequency of transmission wave fB
If the maximum detection speed for is VMAX B and the sampling frequency is fs, then from equation (1),

[0023] VMAX A = C·fs/4fA VMAX B = C·fs/4fB. Therefore, when a plurality of different ultrasonic frequencies are used, the maximum detection speed for each frequency takes a different value. Figure (a) shows this relationship. Next, consider the case where the ratio between the transmitted ultrasound frequency and the sampling frequency is kept constant.

Figure (b) shows the case where the ratio of the transmitted ultrasonic frequency to the sampling frequency is kept constant. Maximum detection speed VMAX A for transmission ultrasound frequency fA, sampling frequency fsA, maximum detection speed VMAX B for transmission ultrasound frequency fB, sampling frequency fsB
Then, from equation (1),

[0025] VMAX A = C・fsA /4fA VMAX B
=C・fsB/4fB (2). Therefore, fsA /4fA = fsB /4fB (3)
If so, the maximum detection speed at each transmission frequency can be set equal. However, when the sampling frequency is set to satisfy equation (3), the time series data of the Doppler shift components for the ultrasound frequencies fA and fB are multiplied by a window function with the same time width and characteristics. The points will be different, and the above-mentioned ratio of Doppler spectrum signal intensities cannot be obtained.

[0026] Therefore, regarding the window function used in the present invention,
This will be explained with reference to FIG. Figure 5 shows, as an example, fB = 2f
A, that is, fsA = 2fsB, the number of sample points is set to 1
The window function WC (n) of the RAISEDCOSIN type when performing fast Fourier transform (FFT) with 28 points is shown. In the present invention, time series data of Doppler shift components are windowed using a window function as shown in the figure.

The illustrated window function is expressed by the following equation. (A) Regarding sampling data for fsA, Wc(n)=0.5-0.5COS(2πn/128
)・・・・・・・・・・・・(4) −127≦n≦0 (B) Regarding the sampling data for fSB, W
c(n)=0.5-0.5COS(2πn/128-1
27≦n≦0 Wc(n)=0 ・・・・・・・・・(5)-255
≦n≦−128 Windowing is performed while moving the window functions of equations (4) and (5) over the time series data of the Doppler shift component. By doing so, data with the same time width can be used, and even in cases such as accelerated flows, coloring can be performed correctly.

FIG. 6 shows an embodiment of the signal synthesis section of the present invention. The figure shows an example in which the hue is determined by the value of the Doppler spectrum signal intensity ratio (PAn/PBn) from the n-th blood flow after velocity conversion, and the brightness is determined by the sum of the intensities (PAn+PBn). 62 is a brightness calculation unit,
63 is a brightness conversion unit, and 64 is a low threshold pass filter (LPF) for determining the sum of scattering intensities (PAn+PBn).

Reference numeral 65 denotes an intensity ratio calculation unit, which calculates the intensity ratio (PAn/PBn) of the Doppler spectrum signal, and 66 denotes a hue conversion unit, which calculates the intensity ratio of the Doppler spectrum signal. Determined hue table (described later)
, which determines the hue, and 67 is a low threshold pass filter (
LPF). 68 is a digital scan converter (
69 is a display device (CRT). Reference numeral 70 denotes a Δ adjustment section for level shifting the Doppler spectrum signal strength, and the setting may be done manually or automatically. Further, when three or more types of transmission ultrasonic frequencies are used, the reflected wave of any one ultrasonic frequency may be shifted by Δ, and the others may be fixed. Note that the cutoff frequency of the low threshold pass filter 64 for luminance is higher than that of the low threshold pass filter 67 for hue. FIG. 7 shows an embodiment of the brightness determination method. Figure (a) shows the intensity of the Doppler spectrum signal for fA, and Figure (b) shows the Doppler spectrum signal for fB. Figure (c) shows the sum of spectra when the sum of Doppler spectrum signal intensities is used as a luminance signal. Figure (d) shows a spectrum when the intensity of a single Doppler spectrum signal is taken as the brightness.

FIG. 8 shows an example of a hue table for color display and a sonogram display according to the present invention. Figure (a) is an example of a hue table. In the figure, the horizontal axis is the Doppler spectrum signal intensity of the blood flow at the n-th position in the depth direction after velocity conversion as PAn, PBn, and the ratio is taken. If PAn/PBn = 1, white It is. PAn/
If PBn<1, it is displayed in red and PAn/PBn
If >1, display in blue. Also, PAn+PB
The brightness level is determined by n. Further, the brightness level may be set to either PAn or PBn as shown in FIG. 7(d), and the hue may be an intermediate phase depending on the value of PAn/PBn.

FIG. 8(b) shows an example of a sonagram display according to the present invention. In the figure, the horizontal axis is time and the vertical axis is blood flow velocity. The figure shows a method in which two different ultrasound frequencies are transmitted to a subject like the one shown in Figure 2(a), the blood flow velocity is determined by the Doppler shift component, and the color and brightness are calculated based on the Doppler spectrum signal strength. This shows the case where it is determined and displayed. The blood flow velocity v1 of blood vessel 1 is displayed in red, and the velocity v2 of blood vessel 2 is displayed in blue. As described above, according to the present invention, the blood flow velocities in blood vessel 1 and blood vessel 2 can be identified and displayed in different colors.

[0032]

[Effects of the Invention] According to the present invention, by using continuous wave ultrasound, the velocity of an object to be examined can be displayed as an image at a high maximum detection speed so that the relative positional relationship of the spatial distribution of the object can be seen. I can do it.

[Brief explanation of the drawing]

FIG. 1 shows a basic configuration diagram of the present invention.

FIG. 2 is an explanatory diagram of the principle of determining the spatial distribution of measurement positions according to the present invention.

FIG. 3 is an explanatory diagram of the measurement position determination principle.

FIG. 4 is a diagram showing the relationship between sampling frequency and maximum detection speed.

FIG. 5 is an explanatory diagram of a window function.

FIG. 6 is a diagram showing an embodiment of a signal combining section of the present invention.

FIG. 7 shows an embodiment of the brightness determination method of the present invention.

FIG. 8 is a diagram showing an example of a hue table and a sonogram display according to the present invention.

FIG. 9 is a diagram showing a conventional continuous wave Doppler ultrasound diagnostic apparatus.

[Explanation of symbols]

1: Ultrasonic probe, 2: Subject, 3, 4: Blood vessel, 5, 5': Continuous wave Doppler section, 7: Signal synthesis section, 8: Transmission drive circuit, 9, 9': Transmission circuit, 10: Reception Drive circuit, 11: Doppler frequency component extraction circuit, 12, 12': sampling circuit, 13: intensity ratio calculation section, 14: hue conversion section, 15: display control section, 16: display device, 17: Δ adjustment section. 100, 100': means for transmitting ultrasonic continuous waves, 10
1,101': means for outputting a Doppler spectrum signal.

Claims (6)

[Claims] [Claim 1] By injecting a plurality of continuous ultrasonic waves with different frequencies into an object (2) containing a moving fluid (3, 4) inside, and analyzing the spectrum of the Doppler-shifted reflected waves in the fluid. , in an ultrasonic diagnostic apparatus for diagnosing the moving speed of fluid inside a subject, a means for transmitting a plurality of continuous ultrasonic waves having different frequencies (100, 10
0'), and means (101, 101') for receiving the reflection from the object, analyzing the spectrum of each reflected wave, and outputting a plurality of Doppler spectrum signals corresponding to the transmission frequency.
and a signal synthesis unit that calculates the ratio of data corresponding to the same velocity of the plurality of Doppler spectrum signals and determines the color when displayed on the screen according to the value of the ratio, up to a predetermined depth, An ultrasonic diagnostic apparatus characterized in that a sonogram display of a moving fluid in a deeper part can be distinguished by a difference in color. Claim 2: Means for transmitting ultrasonic continuous waves (100
, 100') and means (101, 101') for outputting a Doppler spectrum signal.
5 and 5') respectively sample each Doppler component at the same sampling frequency, and obtain a spectrum by Fourier transforming the sampled time series signal. . [Claim 3] The continuous wave Doppler section (5, 5') sets the maximum detection speed at each transmitting ultrasound frequency by keeping the ratio of each transmitting ultrasound frequency and its corresponding sampling frequency constant. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein the spectrum is created by sampling the Doppler component equally to , and Fourier transforming the sampled time series signal. 4. The apparatus according to claim 1, 2, or 3, further comprising an adjustment section capable of weighting each transmission frequency for at least one of the transmission ultrasound, the mixer signal, the Doppler signal, or the Doppler spectrum signal. The ultrasonic diagnostic device according to any one of the above. 5. Any one of claims 1, 2, 3, or 4, characterized in that the hue is determined according to the value of the ratio of each Doppler spectrum signal, and the sum of the intensities of the respective Doppler spectrum signals is defined as the brightness. The ultrasonic diagnostic device described in . 6. The method of claim 1, 2, 3 or 3, wherein the hue is determined according to the value of the ratio of each of the Doppler spectrum signals, and one of the intensities of the Doppler spectrum signals is selected as the brightness. 4. The ultrasonic diagnostic apparatus according to any one of 4. 0001