KR20170075363A - Ultrasound system and method of displaying doppler spectrum image - Google Patents

Abstract

The ultrasound system includes an ultrasonic probe, a processor, and a display unit. The ultrasonic probe transmits an ultrasonic signal to a target object and receives an ultrasonic echo signal reflected from the target object based on a Doppler gate set at a predetermined position of the B-mode image of the object. The processor forms a Doppler signal based on the ultrasound echo signal, forms a Doppler signal envelope representing the Doppler signal with a plurality of brightness values, determines a trace rate indicative of a maximum velocity of the Doppler signal based on the Doppler signal envelope, Filters the noise in the Doppler signal based on the velocity, and forms a Doppler spectrum image of the object based on the filtered Doppler signal. The display unit displays a Doppler spectrum image.

Description

TECHNICAL FIELD [0001] The present invention relates to an ultrasound system and a method for displaying a Doppler spectrum image,

The present disclosure relates to an ultrasound system, and more particularly to an ultrasound system and method for displaying Doppler spectrum images.

Ultrasound systems have non-invasive and non-destructive properties and are widely used in the medical field to obtain information inside objects. Without the need for surgical intervention to directly observe the subject, the ultrasound system can provide the physician with high resolution images of the object in real time. Thus, ultrasound systems have become an important tool for diagnosing various diseases.

The ultrasound system transmits an ultrasound signal to a target object and receives an ultrasound signal reflected from the target object (i.e., an ultrasound echo signal) to form an ultrasound image. The ultrasound echo signal represents a different pattern depending on whether the object of interest of interest is stationary or moving. For example, when the object of interest of the object is moving toward the ultrasonic probe (i.e., ultrasonic transducer) side of the ultrasonic system, the ultrasonic echo signal reflected from the object of interest has a relatively higher frequency than when the object of interest is stationary. On the other hand, when the object of interest is away from the ultrasound probe of the ultrasound system, the ultrasound echo signal reflected from the object of interest has a relatively low frequency as compared to the case where the object of interest is stopped. That is, a Doppler shift occurs in an ultrasonic echo signal reflected from a moving object of interest of the object. The ultrasonic system can obtain the Doppler signal including the velocity information about the object of interest of the object using the Doppler deviation, and display the obtained Doppler signal as a continuous spectrum (i.e., Doppler spectrum image) on the display unit.

The ultrasound system traces the maximum velocity of the object of interest based on the acquired velocity information and provides a trace process that displays the traced maximum velocity as a line. However, in conventional ultrasound systems, it may be difficult to accurately trace the maximum velocity of the object of interest if there is aliasing on the Doppler spectrum image.

On the other hand, the Doppler signal includes noise (for example, system noise) as well as a signal indicating speed information of the object of interest. Therefore, in the conventional ultrasonic system, when the gain is adjusted, there is a problem that the noise (e.g., system noise) increases or decreases together with the signal indicating the velocity information of the object of interest.

The present disclosure provides embodiments of an ultrasound system and method for forming a Doppler signal envelope based on a Doppler signal of a subject and determining a trace rate based on the formed Doppler signal envelope. The present disclosure also provides embodiments of an ultrasound system and method for removing noise from a Doppler signal based on a determined trace rate.

An ultrasonic probe configured to transmit an ultrasonic signal to the object based on a Doppler gate set at a predetermined position of the B mode image of the object and to receive the ultrasonic echo signal from the object; A Doppler signal envelope is formed on the basis of the Doppler signal envelope, the Doppler signal envelope representing the Doppler signal as a plurality of brightness values is formed, a trace speed indicating a maximum speed of the Doppler signal is determined based on the Doppler signal envelope, A processor configured to filter a noise in the Doppler signal based on the filtered Doppler signal and to form a Doppler spectrum image of the object based on the filtered Doppler signal; and a display unit configured to display the Doppler spectrum image, do.

In another embodiment, a method of forming a Doppler spectrum image of a subject in an ultrasound system is provided. The method includes the steps of obtaining a Doppler signal based on a Doppler gate set at a predetermined position of a B mode image of a target object, forming a Doppler signal envelope representing the Doppler signal with a plurality of brightness values, Determining a trace rate that represents a maximum velocity of the Doppler signal based on the detected velocity; filtering noise in the Doppler signal based on the trace velocity; and performing a Doppler spectral image of the object on the basis of the filtered Doppler signal. And displaying the Doppler spectrum image.

According to some embodiments of the present disclosure, even if there is aliasing in the Doppler spectrum image of the object, it is possible to accurately trace the maximum velocity of the object of interest within the object. Further, according to some embodiments of the present disclosure, noise may be removed from the Doppler signal based on the determined trace rate. Thus, when the gain is adjusted, only the signal representing the velocity information of the object of interest can be increased or decreased.

1 is a block diagram schematically showing a configuration of an ultrasound system according to an embodiment of the present disclosure;
2 shows an example of a Doppler spectrum image according to an embodiment of the present disclosure;
3 is a block diagram schematically illustrating a configuration of a processor according to an embodiment of the present disclosure;
4 illustrates an example of a Doppler gate according to an embodiment of the present disclosure;
5 illustrates an example of a Doppler signal envelope according to an embodiment of the present disclosure;
6 illustrates an example of a first trace start line according to an embodiment of the present disclosure;
7 illustrates an example of a second trace start line and a trace rate in accordance with an embodiment of the present disclosure;
8 illustrates an example of a trace line according to an embodiment of the present disclosure;
9 is a flow diagram illustrating a procedure for displaying a Doppler spectrum image in accordance with an embodiment of the present disclosure;

Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The term "part " used in the present embodiment means hardware components such as software, field-programmable gate array (FPGA), and application specific integrated circuit (ASIC). However, "part" is not limited to software and hardware. "Part" may be configured to reside on an addressable storage medium, and may be configured to play back one or more processors. Thus, by way of example, and not limitation, "part, " as used herein, is intended to be broadly interpreted as referring to components such as software components, object-oriented software components, class components and task components, Firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided within the component and the "part " may be combined into a smaller number of components and" parts " or further separated into additional components and "parts ".

1 is a block diagram schematically showing a configuration of an ultrasound system according to an embodiment of the present disclosure. The ultrasound system 100 includes a control panel 110, an ultrasound probe 120, a processor 130, a storage unit 140, and a display unit 150. In this embodiment, the processor 130 controls the control panel 110, the ultrasonic probe 120, the storage unit 140, and the display unit 150.

The control panel 110 receives the input information from the user and transmits the received input information to the processor 130. The control panel 110 may include an input (not shown) that enables an interface between the user and the ultrasound system 100 and / or allows the user to manipulate the ultrasound system 100. The input unit may include an input device suitable for performing operations such as selection of a diagnostic mode, control of a diagnostic operation, input of a command necessary for diagnosis, signal operation, output control, and the like, for example, a track ball, a keyboard, a button and the like.

The ultrasonic probe 120 includes an ultrasonic transducer (not shown) configured to mutually convert an electric signal and an ultrasonic signal. The ultrasonic probe 120 converts an electric signal (hereinafter referred to as a "transmission signal") provided from the processor 130 into an ultrasonic signal and transmits the ultrasonic signal to the object. The object includes an object of interest (e.g., blood flow, vessel wall, etc.). The ultrasonic probe 120 receives an ultrasonic signal (that is, an ultrasonic echo signal) reflected from the object and converts the ultrasonic echo signal into an electrical signal (hereinafter referred to as a "reception signal").

In response to the input information received through the control panel 110, the processor 130 may control the ultrasonic probe 120 to transmit the ultrasonic signal to the object and receive the ultrasonic echo signal reflected from the object. The processor 130 forms a Doppler signal of the object and one or more ultrasound images (for example, a brightness mode image, a Doppler spectrum image, etc.) based on the reception signal provided from the ultrasonic probe 120 can do.

In one embodiment, the processor 130 determines the velocity of the object of interest in a continuous spectral line based on the received signal provided from the ultrasonic probe 120, in real time, The Doppler spectrum image 210 shown in FIG. 2, a newly formed spectral line is displayed on the right side of the Doppler spectrum image 210. In Fig. The spectral lines are moved / scrolled from right to left. That is, previously formed spectral lines are moved or scrolled from right to left, and newly formed spectral lines are displayed on the right. 2, the reference numeral 220 indicates a base line, the numeral 230 denotes a higher spectral line, a reference numeral 240 denotes a lower spectral line, V _{pre _max} indicates a pre-set maximum speed scale, V _{pre _min} represents a preset minimum speed scale.

The storage unit 140 sequentially stores the reception signals formed by the ultrasonic probe 120 on a frame-by-frame basis. The storage unit 140 sequentially stores the Doppler signals generated by the processor 130. In addition, the storage unit 140 stores one or more ultrasound images formed by the processor 130. In addition, the storage unit 140 may store instructions for operating the ultrasound system 100.

The display unit 150 displays one or more ultrasound images (for example, B mode image, Doppler spectrum image, etc.) formed in the processor 130. In addition, the display unit 150 may display appropriate information regarding the ultrasound image or the ultrasound system 100.

3 is a block diagram schematically illustrating a configuration of a processor 130 according to an embodiment of the present disclosure. The processor 130 includes a transmitter 310. The transmitting unit 310 forms a transmission signal for obtaining an ultrasound image of a target object. 4, the transmitting unit 310 forms a transmission signal for obtaining a Doppler signal corresponding to the Doppler gate 420 set at a predetermined position of the B mode image 410 of the object . 4, reference numeral 430 denotes a blood vessel wall. The transmission signal is provided to the ultrasonic probe 120. The ultrasonic probe 120 converts a transmission signal into an ultrasonic signal, and transmits the ultrasonic signal to the object. Further, the ultrasonic probe 120 receives the ultrasonic echo signal reflected from the object and forms a reception signal.

Referring again to FIG. 2, the processor 130 further includes a transmission / reception switch 320 and a reception unit 330. The transmission / reception switch 320 serves as a duplexer for switching the transmission unit 310 and the reception unit 330. For example, when the ultrasonic probe 120 performs transmission and reception alternately, the transmission / reception switch 320 appropriately transmits the transmission unit 310 or the reception unit 330 to the ultrasonic probe 120 (i.e., the ultrasonic transducer) Switching or electrical connection.

In the processor 130, the receiver 330 amplifies the received signal received from the ultrasonic probe 120 through the transmit / receive switch 320, and converts the amplified received signal into a digital signal. The receiver 330 includes a time gain compensation (TGC) unit (not shown) for compensating for the attenuation that occurs when the ultrasonic signal passes through the object, an analog-to-digital conversion (analog to digital conversion) unit (not shown), and the like.

The processor 130 further includes a signal forming unit 340. [ The signal forming unit 340 performs beamforming on a digital signal provided from the receiving unit 330 to form a receive focusing signal. The signal forming unit 340 forms a Doppler signal corresponding to the Doppler gate 420 based on the receive focusing signal.

The processor 130 further includes a signal processor 350. The signal processing unit 350 determines a trace rate for tracing the maximum velocity of the blood flow in the Doppler gate 420 based on the Doppler signal provided from the signal forming unit 340. In addition, the signal processing unit 350 filters noise from the Doppler signal based on the determined trace rate.

In one embodiment, the signal processing unit 350 forms a Doppler signal envelope representing a Doppler signal provided from the signal forming unit 340 as a plurality of brightness values. For example, as shown in FIG. 5, the signal processing unit 350 forms a Doppler signal envelope 530 corresponding to the spectral line 510 based on the Doppler signal provided from the signal forming unit 340 . In Fig. 5 (a), the horizontal axis represents time and the vertical axis represents speed. 5 (b), the horizontal axis represents velocity and the vertical axis represents brightness (intensity). That is, the Doppler signal envelope 520 may be an envelope representing the Doppler signal present on the line between the base 220 and the pre-set maximum speed scale _(pre V _{_max)} into a plurality of brightness (intensity) value.

The signal processing unit 350 determines a peak of the generated Doppler signal envelope 520. 5, the signal processing unit 350 determines the maximum brightness value in the Doppler signal envelope 520 and determines the determined maximum brightness value as the peak 530 of the Doppler signal envelope 520, for example, do.

The signal processing unit 350 determines a threshold value for estimating noise in the Doppler signal envelope 520 based on the determined peak 530. [ As an example, the signal processing unit 350 determines, as a threshold value, any one of the brightness values in a range of 30 to 60% of the determined peak 530 (i.e., the maximum brightness value), as shown in FIG. As another example, the signal processing unit 350 determines a threshold value 540 as a brightness value in a range of 50% of the determined peak 530.

The signal processing unit 350 determines the trace rate of the Doppler signal based on the Doppler signal envelope 520 and the threshold value 540. For example, the signal processing below 350, the threshold value 540 at the predetermined maximum speed scale Doppler signal envelope 520 between (V _{pre _max)} and the base line 220, as shown in Figure 6 And selects the corresponding Doppler signal envelope (see the one-dot chain line in FIG. 6). The focus of the signal processing unit 350 (see a chain line in Fig. 6) selected Doppler signal envelope (X _c1) [that is, a preset maximum speed scale (V _{pre_max)} and emphasis between X _1] a, and the determined focus determination based on the (X _c) determines a first trace start line 610. Then, the signal processing unit 350, as illustrated in Figure 7, the pre-set maximum speed scale (V _{pre _max)} of the first trace start line 610, a Doppler signal envelope goes below the threshold value 540 at 520 between (See the chain double-dashed line in Fig. 7) corresponding to the Doppler signal envelope. The signal processing unit 350 determines the midpoint X _c2 (that is, the midpoint between the preset maximum velocity scale V _{pre_max} and X ₂ ) of the selected Doppler signal envelope (see the chain _double- dashed line in FIG. 7) The second trace start line 710 is determined based on the second trace start line X _c2 . The signal processor 350 then performs a trace operation on the Doppler signal envelope 520 to determine the trace rate from the second trace start line 710 to the baseline 220 so that the threshold 540 is first exceeded The brightness value 720 is determined. The signal processing unit 350 determines the speed corresponding to the determined brightness value 720 as the Doppler signal trace rate. The determined trace rate may be displayed as a trace line 810 in the Doppler spectrum image 210, as shown in FIG.

In another embodiment, the signal processor 350 may filter noise (e.g., impulsive noise) above a predetermined rate (e.g., 200%) of the determined trace rate. As an example, the signal processing unit 350 may include an intermediate value filter (not shown) having a predetermined size. That is, the signal processing unit 350 selects a trace rate corresponding to the current Doppler signal (hereinafter referred to as a "current trace rate"). The signal processing unit 350 selects a trace rate (hereinafter, referred to as "previous trace rate") corresponding to the Doppler signal before the current Doppler signal, based on the current trace rate. The previous trace rate is determined according to the predetermined size of the median filter. The signal processing unit 350 determines the trace rate of the intermediate value in the sorted trace rate and the trace rate of the current Doppler signal in the ascending order of the current trace rate and the previous trace rate. As another example, the signal processing unit 350 may include a moving average filter having a predetermined size. That is, the signal processor 350 selects the current trace speed corresponding to the current Doppler signal. The signal processor 350 selects the previous trace rate corresponding to the Doppler signal before the current Doppler signal, based on the current trace rate. The previous trace rate may be determined according to a predetermined size of the moving average filter. The signal processor 350 determines the average trace rate of the current trace rate and the previous trace rate, and determines the average trace rate as the trace rate corresponding to the current Doppler signal.

In another embodiment, the signal processing unit 350 filters noise (e.g., system noise) in the Doppler signal based on the determined trace rate. For example, the signal processing section 350 determines a threshold value (hereinafter referred to as a "filtering threshold value") for filtering the noise by applying a predetermined value to the determined trace speed. As an example, the signal processing section 350 determines a filtering threshold value in a range of 80 to 120% of the determined trace rate. The signal processing unit 350 filters the Doppler signal corresponding to the speed exceeding the filtering threshold as noise.

Although it has been described as determining the trace rate for the upper spectral line 230 and filtering the noise, it is also possible to filter the trace rate and noise in a similar manner for the lower spectral line 240.

Referring again to FIG. 3, the processor 130 further includes an image forming unit 360. The image forming unit 360 forms a spectral line, that is, a Doppler spectrum image, based on the Doppler signal filtered by the signal processing unit 350. 8, the shape-forming unit 360 forms a trace line 810 based on the trace speed determined in the signal processing unit 350. The trace-

9 is a flow chart illustrating a procedure for displaying a Doppler spectrum image according to an embodiment of the present disclosure. The processor 130 obtains a Doppler signal corresponding to the Doppler gate 420 set at a predetermined position of the B mode image 410 of the object (S902).

The processor 130 forms a Doppler signal envelope 520 as shown in FIG. 5 based on the obtained Doppler signal (S904). The processor 130 determines a peak of the Doppler signal envelope 520 (S906). For example, the processor 130 determines the maximum brightness value at the Doppler signal envelope 520 and determines the determined maximum brightness value as the peak of the Doppler signal envelope 520. [

The processor 130 determines a threshold for estimating noise in the Doppler signal based on the peak of the Doppler signal envelope 520 (S908). As an example, the processor 130 determines a threshold value as one of the brightness values in the range of 30 to 60% of the peak of the Doppler signal envelope 520. As another example, the processor 130 determines the threshold value as the brightness value in the range of 50% of the peak of the Doppler signal envelope 520. [

The processor 130 determines a first trace start line based on the Doppler signal envelope and the threshold value (S910). For example, the hereinafter processor 130, as illustrated in Figure 6, the pre-set maximum speed scale (V _{pre _max)} and the baseline threshold 540 in the Doppler signal envelope 520 between 220 Doppler signal envelope (refer to the one-dot chain line in Fig. 6) is selected. The processor 130 determines the midpoint of the selected Doppler signal envelope (see dashed line in FIG. 6), and determines the first trace start line 610 based on the determined midpoint.

The processor 130 determines a second trace start line based on the Doppler signal envelope, the threshold, and the first trace start line (S910). For example, the processor 130 may _{compare the} threshold 540 in the Doppler signal envelope 520 between the predetermined maximum velocity scale (V _{pre -} max) and the first trace start line 610, (See the chain double-dashed line in FIG. 7) corresponding to the following. Processor 130 determines the midpoint of the selected Doppler signal envelope (see dashed line in FIG. 7) and determines a second trace start line 710 based on the determined midpoint.

The processor 130 determines the trace rate of the Doppler signal based on the second trace start line (S914). For example, the processor 130 traces the Doppler signal envelope 520 from the second trace start line 710 to the baseline 220, as shown in FIG. 7, The brightness value 720 is determined. The processor 130 determines the speed corresponding to the determined brightness value 720 as the tracing speed of the Doppler signal.

The processor 130 filters the noise in the Doppler signal based on the determined trace rate (S916). For example, the processor 130 filters the impulse noise in the trace line 810 based on the determined trace rate and filters the system noise in the Doppler signal based on the filtered trace rate.

The processor 130 forms a Doppler spectrum image based on the filtered Doppler signal (S918). The Doppler spectrum image can be displayed on the display unit 150. In addition, the trace rate can be displayed on the display unit 150 as a trace line 810, as shown in FIG.

While specific embodiments have been described, these embodiments are provided by way of illustration and are not to be construed as limiting the scope of the disclosure. The novel methods and apparatus of the present disclosure may be implemented in various other forms, and it is possible to variously omit, substitute, and alter the embodiments disclosed herein without departing from the spirit of the present disclosure. It is intended that the appended claims and their equivalents be interpreted as embracing all such forms and modifications as fall within the scope and spirit of this disclosure.

100: Ultrasonic system 110: Control panel
120: Ultrasonic probe 130: Processor
140: storage unit 150: display unit
210: Doppler spectrum image 220: baseline
310 transmission unit 320 transmission /
330: Receiving unit 340: Signal forming unit
350: signal processing unit 360: image forming unit
410: B mode image 420: Doppler gate
430: blood vessel wall 510: spectral line
520: Doppler signal envelope 530: Peak
540: Threshold
V _{pre _max:} preset maximum speed scale
V _{pre _min:} preset minimum speed scale
610: first trace start line 710: second trace start line
720: trace rate 810: trace line

Claims (18)

A method of displaying a Doppler spectrum image of a target in an ultrasound system,
Acquiring a Doppler signal based on a Doppler gate set at a predetermined position of a B mode image of the object;
Forming a Doppler signal envelope in which the Doppler signal is represented by a plurality of brightness values;
Determining a trace rate representing a maximum rate of the Doppler signal based on the Doppler signal envelope;
Filtering noise in the Doppler signal based on the trace rate;
Forming a Doppler spectrum image of the object based on the filtered Doppler signal;
Displaying the Doppler spectrum image
≪ / RTI > 2. The method of claim 1, wherein determining the trace rate comprises:
Determining a peak of the Doppler signal envelope;
Determining a threshold for estimating the noise in the Doppler signal envelope based on the determined peak;
Determining a trace start position on the Doppler signal envelope based on the threshold;
Determining the trace rate in the Doppler signal envelope based on the trace start position
≪ / RTI > 3. The method of claim 2, wherein determining the threshold comprises:
Determining a brightness value in a range of 30% to 60% of the peak as the threshold value
≪ / RTI > 4. The method of claim 3, wherein determining the threshold comprises:
Determining a brightness value corresponding to a range of 50% of the peak as the threshold value
≪ / RTI > 3. The method of claim 2, wherein determining the trace starting position comprises:
Selecting a first Doppler signal envelope that falls below the threshold value in the Doppler signal envelope;
Determining a first midpoint of the first Doppler signal envelope;
Determining a first trace start position of the Doppler signal envelope based on the first midpoint;
Selecting a second Doppler signal envelope that falls below the threshold value in the Doppler signal envelope based on the first trace start position;
Determining a second midpoint of the second Doppler signal envelope;
Determining a second trace starting position of the Doppler signal envelope based on the second midpoint;
≪ / RTI > 6. The method of claim 5, wherein determining the trace rate comprises:
Determining the trace rate based on the second trace start position of the Doppler signal envelope
≪ / RTI > 2. The method of claim 1, wherein filtering the noise comprises:
Determining a filtering threshold for filtering the noise by applying a predetermined value to the determined trace rate;
Filtering the noise in the Doppler signal based on the filtering threshold
≪ / RTI > 8. The method of claim 7, wherein the filtering threshold comprises a rate in the range of 80% to 120% of the determined trace rate. 9. The method according to any one of claims 1 to 8,
Filtering impulse noise above a predetermined rate of said determined trace rate;
≪ / RTI > As an ultrasound system,
An ultrasonic probe configured to transmit an ultrasonic signal to the object based on a Doppler gate set at a predetermined position of the B-mode image of the object and receive the ultrasonic echo signal from the object;
Forming a Doppler signal based on the ultrasonic echo signal, forming a Doppler signal envelope in which the Doppler signal is represented by a plurality of brightness values, determining a trace speed indicating a maximum velocity of the Doppler signal based on the Doppler signal envelope A processor configured to filter noise in the Doppler signal based on the trace rate and to form a Doppler spectrum image of the object based on the filtered Doppler signal;
A display unit configured to display the Doppler spectrum image,
. 11. The apparatus of claim 10, wherein the processor is further configured to: determine a peak of the Doppler signal envelope; determine a threshold for estimating the noise in the Doppler signal envelope based on the determined peak; And a signal processing unit configured to determine a trace start position on the Doppler signal envelope and to determine the trace rate on the Doppler signal envelope based on the trace start position. 12. The ultrasound system of claim 11, wherein the processor is configured to determine, as the threshold, any one of brightness values in the range of 30% to 60% of the peak. 13. The ultrasound system of claim 12, wherein the processor is configured to determine a brightness value in the range of 50% of the peak as the threshold value. 11. The apparatus of claim 10, wherein the processor is further configured to: select a first Doppler signal envelope that is less than or equal to the threshold value in the Doppler signal envelope, determine a first midpoint of the first Doppler signal envelope, Determines a first trace start position of the Doppler signal envelope based on the first trace start envelope and selects a second Doppler signal envelope corresponding to the threshold value or less from the Doppler signal envelope based on the first trace start position, And a signal processing unit configured to determine a second midpoint of the signal envelope and to determine a second trace start position of the Doppler signal envelope based on the second midpoint. 15. The ultrasound system of claim 14, wherein the processor is configured to determine the trace rate based on the second trace start position of the Doppler signal envelope. 11. The apparatus of claim 10, wherein the processor is further configured to: apply a predetermined value to the determined trace rate to determine a filtering threshold for filtering the noise, and to filter the noise in the Doppler signal based on the filtering threshold And a signal processing unit configured to receive the ultrasonic signal. 17. The ultrasound system of claim 16, wherein the filtering threshold comprises a rate in the range of 80% to 120% of the determined trace rate. 18. The ultrasound system of any one of claims 10 to 17, wherein the processor is further configured to filter impulse noise above a predetermined rate of the determined trace rate.

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