Disclosure of Invention
The shear wave imaging method and the shear wave imaging system are provided, the signal to noise ratio of detection is improved, the redundant detection times are reduced, and the detection process is accelerated.
A shear wave imaging method comprising the steps of,
generating shear waves within the tissue;
estimating the positions of the shear waves at different moments, sending a plurality of tracking pulses corresponding to the positions of the shear waves at different moments, and receiving echo information of the tracking pulses;
calculating the parameters of the shear wave according to the echo information of the tracking pulse;
and imaging and displaying the result of the shear wave parameter calculation.
Further, when estimating the shear wave, transmitting a plurality of tracking pulses corresponding to the positions of the shear wave at different time instants and receiving echo information of the tracking pulses, further comprising the following steps,
estimating the propagation speed of the shear wave in the target tissue;
estimating the estimated shear wave position of the shear wave in the target tissue at each moment according to the propagation speed of the shear wave in the target tissue;
and respectively sending tracking pulses to the corresponding shear wave estimation positions at each moment, and receiving echo information of each tracking pulse.
Further, when the estimated position of the shear wave at each moment is obtained, the position distance of the shear wave from the wave source is obtained
Satisfies the following conditions:
wherein, t is
k At any time after the generation of the shear wave, t
0 For the moment of initial propagation of the shear wave,
is the average velocity of the shear wave propagating within the target tissue.
Further, the moving distance of the detection position of the shear wave between two adjacent detection times is less than or equal to ch Δ t, and the detection width of the shear wave at each detection is greater than or equal to Δ t (c)h -cl ) Wherein the variation range of the estimated shear wave velocity is cl To ch And delta t is the time interval between two adjacent detection moments.
Further, when shear wave parameters are calculated based on the echo information of the tracking pulse, at least one of the propagation distance of the shear wave, the propagation velocity of the shear wave, and the young's modulus of the target tissue is calculated.
Further, when calculating the shear wave parameters according to the echo information of the tracking pulse, the method further comprises the following steps:
setting reference information;
and performing cross-correlation comparison on the echo information of the tracking pulse at different moments of each position in the target area and the reference information corresponding to the position to acquire particle displacement data at the position at different moments.
Further, when the reference information is set, the echo information of the tracking pulse at a certain time is selected as the reference information or the reference pulse is sent before the shear wave is propagated, and the echo information of the reference pulse is used as the reference echo information.
Further, when shear wave parameters are calculated according to the echo information of the tracking pulse, the propagation velocity of the shear wave satisfies the following formula:
wherein c represents a propagation velocity, uz It can be considered as longitudinal displacement data, or it can be calculated using longitudinal velocity data, x representing the lateral coordinate and z representing the longitudinal coordinate.
Further, when the result of the shear wave parameter calculation is displayed in an imaging mode, at least one of a propagation velocity distribution diagram, a young modulus parameter diagram, a shear modulus parameter diagram, a propagation distance parameter diagram in a certain period of time, and an average velocity value parameter diagram in a target region is formed.
A shear wave imaging system comprises an ultrasonic probe, a control module, a signal processing module, a calculation module and a display system, wherein the ultrasonic probe is provided with a transceiver module, the signal processing module, the calculation module and the display system of the ultrasonic probe are sequentially connected, the control module is connected with the transceiver module,
the receiving and transmitting module is used for transmitting a tracking pulse according to the estimated position of the shear wave and receiving echo information of the tracking pulse and the reference pulse;
the control module is used for controlling the transceiver module to transmit the tracking pulse;
the signal processing module is used for carrying out signal preprocessing on the echo information;
the computing module is used for predicting the predicted positions of the shear waves at different moments and processing and computing the signals output by the signal processing module;
the display system is used for displaying the image of the calculation result of the shear wave parameters generated by the calculation module.
Further, the calculation module comprises a calculation module,
and the estimation unit is used for estimating the estimated position of the shear wave at each moment according to the propagation time of the shear wave and the average propagation speed of the shear wave in the target tissue.
And the data calculation unit is used for calculating the propagation parameters of the shear wave.
According to the shear wave imaging method and system provided by the invention, the detection position of the shear wave is estimated in advance, so that the detection of the shear wave can be accurately carried out in a small range, the detection energy is relatively concentrated, and the detection signal-to-noise ratio is improved. Meanwhile, the redundant detection times are reduced, the detection process is accelerated, and the data processing burden is reduced.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a shear wave imaging method according to a preferred embodiment of the present invention pre-estimates a detection position of a shear wave, so that the detection of the shear wave can be accurately performed in a small range, and thus, the detection energy is relatively concentrated, and the detection signal-to-noise ratio is improved. Meanwhile, the redundant detection times are reduced, the detection process is accelerated, and the data processing burden is reduced.
The shear wave imaging method of the present invention comprises the steps of:
step S101, generating shear waves in the tissue. In this step, various methods can be used to generate shear waves inside the tissue, such as generating shear waves inside the tissue by external force vibration outside the tissue, generating shear waves inside the tissue by emitting acoustic radiation force pulses (ARFI) into the tissue, and the like. Wherein the acoustic radiation force pulses may or may not be focused.
It can be understood that, because the amplitude of the shear wave generated by emitting the acoustic radiation force pulse is relatively small, and because the shear wave can be rapidly attenuated along with propagation, the intensity of the shear wave can be improved by emitting a series of acoustic radiation force pulses, or the propagation range of the shear wave can be widened, or the detection sensitivity can be improved by changing the waveform characteristics of the shear wave, so as to avoid the influence on the imaging due to the attenuation of the shear wave.
As shown in fig. 2, multiple focused pulses may be transmitted sequentially to the same location to increase the intensity of the generated shear wave. As shown in fig. 3 and 4, the longitudinal (referring to the direction of focused transmission) and transverse (referring to the direction perpendicular to the focused transmission) positions of the continuously transmitted focused pulses can be changed to widen the propagation range of the shear wave and make the shear wave propagate along a specific direction. As shown in fig. 5, pulses may be transmitted simultaneously at different lateral positions so that two shear waveforms arriving at different times in succession are superimposed for ease of detection.
And S102, estimating the positions of the shear waves at different moments, sending a plurality of tracking pulses corresponding to the positions of the shear waves at different moments, and receiving echo information of the tracking pulses.
The step S102 further includes the steps of:
step S1021, estimating the propagation speed of the shear wave in the target tissue.
After the shear wave is generated, the shear wave starts to propagate in the tissue, and the propagation speed is different along with the difference of the elastic characteristics of the tissue. To predict the pursuit shear wave, it is necessary to estimate an average velocity from the target tissue
And estimating a possible speed variation range c
l To c
h This average speed and range may be pre-specified by the system on a case-by-case basis with reference to existing academic measurement data, or measurement experience, and the like. For example, the average propagation velocity of the shear wave in the target tissue is assumed to be about 2m/s, and the possible variation range is 1-4 m/s, or the average propagation velocity is assumed to be 1m/s, and the possible variation range is 0.5-2 m/s.
Step S1022, estimating the position of the shear wave in the target tissue at each time according to the propagation speed of the shear wave in the target tissue, and obtaining the estimated position of the shear wave at each time.
At different times t after the generation of the shear wave
k Assuming the initial propagation time t of the shear wave
0 Then the position distance from the wave source can be estimated
Satisfies the following relation:
assuming that the time interval between two adjacent detection moments is Δ t, the following conditions are satisfied: Δ t = tk -tk-1 Then the propagation range Δ d of the shear wave between two detection instants can be estimatedl ~Δdh Satisfies the following conditions:
Δdl =cl Δt
Δdh =ch Δt
then, the moving distance of the shear wave detection position between the two adjacent detection times is less than or equal to Δ dl The estimated positioning advance is avoided when the shear wave propagation is too slow, and the detection width of the shear wave is more than or equal to delta d during each detectionh -Δdl =Δt(ch -cl ) So as to ensure that each estimated positioning can include all possible positions of the shear wave at the moment.
Step S1021, respectively sending tracking pulse to the corresponding estimated shear wave position at each moment, and receiving echo information of each tracking pulse.
As shown in fig. 6, starting from the beginning of the propagation of the shear wave, the system sends tracking pulses at an interval Δ t to continue the detection, and each detection maintains a certain detection transverse beam width, i.e. simultaneously retrieves a certain width of echo information, which includes information of each transverse position in the certain width, and the interval of the transverse positions cannot be too large to ensure a certain transverse resolution. At the same time, the beam center remains less than Δ d between adjacent detectionsl Or if Δ t is small, results in Δ dl Too small is also equivalent to keeping the beam center distance smaller than n Δ d between every n detection instantsl The moving distance of (2). Of course, the system may start detection from any time or from a distance from the shear wave source, and only needs to estimate the possible location of the shear wave at the current location or at the current time according to the average propagation velocity, and needs to start changing the center location of each detection after the shear wave is transmitted to and departed from the location.
Since each detection must maintain a certain lateral beam width and the lateral line spacing cannot be too large to ensure a certain lateral resolution, it may be desirable to have an ultra-wide beam-forming capability, i.e., the ability to recover echo information for multiple lateral positions simultaneously, as shown in fig. 7 and 8. The number of beams is, for example, 1 to 1024, and the system is adjusted as needed, for example, 4 beams, 16 beams, 32 beams, 64 beams, 96 beams, 128 beams, and the like. The wider the beam, the weaker the focus of the transmitted sound field is, the more uniform and less concentrated the lateral distribution of the sound field energy is, which also brings about a reduction in the signal-to-noise ratio of each detection position in the beam. In order to improve the detection quality, the same central position can be continuously transmitted for a plurality of times, the angle of each transmitted beam is different, and then echo signals of different angles are synthesized to increase the signal to noise ratio. The number of the angles and the size of the deflection angle are adjusted by the system according to actual needs, for example, 3 angles, deflection-5 degrees, 0 degrees, 5 degrees and the like are adopted.
And step S103, calculating shear wave parameters according to the echo information of the tracking pulse. From the echo information of the tracking pulse, various parameters such as propagation distance, propagation velocity, young's modulus, etc. can be calculated.
In this step, the echo information of the tracking pulse at each time can be integrated, so as to obtain the echo information of the shear wave in a short period of time at each position of the target tissue in the propagation process, and the shear wave just passes through the corresponding position in the short period of time.
The step S103 further includes the steps of:
step S1031, acquiring reference information; it is to be understood that the reference information may be selected as desired. For example, the echo information of the tracking pulse at a certain time at the corresponding position is selected as the reference information. It is also possible to send a reference pulse before the propagation of the shear wave and to use the echo information of the reference pulse as reference echo information. The reference needs to be used for cross-correlation comparison with the tracking pulse that chases the shear wave.
Step S1032 performs cross-correlation comparison between the echo information of the tracking pulse at each position in the target area at different time and the reference information corresponding to the position, and acquires particle displacement data at the position at different time. Further, a displacement versus time curve may be developed at the location, during which time the shear wave may undergo the entire process of approaching, arriving at, and leaving the location, corresponding to the appearance of a peak in the curve. As shown in fig. 5, due to the pre-estimated chase detection, each lateral position can obtain a corresponding small displacement-time curve, but the corresponding time of the curve is different, and the corresponding time of adjacent positions may have a part of overlap. The position of the peak on the displacement-time curve corresponds to the time at which the shear wave reaches that position.
For example, the propagation velocity of the shear wave may be calculated by performing a cross-correlation comparison on displacement-time curves corresponding to two different lateral positions at the same depth to obtain a time difference corresponding to the propagation time of the shear wave between the two lateral positions. The ratio of the distance between the transverse positions to the propagation time is the propagation velocity between the two transverse positions.
For example, for a certain position, the displacement data of each transverse position corresponding to two times near the time when the shear wave reaches the position are extracted to form displacement-transverse position curves at the two times, and the transverse position difference between the two times can be obtained by performing cross-correlation comparison on the two curves, wherein the position difference corresponds to the propagation distance of the shear wave between the two times. The ratio of the propagation distance to the time difference between the two moments is the propagation velocity near the location.
For example, the approximate calculation formula can be derived directly from the wave propagation equation as follows:
wherein c represents a propagation velocity, uz It can be considered longitudinal displacement data, and it can also be calculated using longitudinal velocity data, x representing the lateral coordinate and z representing the longitudinal coordinate. The above formula can also be transformed into the frequency domain for calculation.
Under certain conditions, the propagation velocity of shear waves has an approximately fixed relationship to tissue stiffness:
E=3ρc2
where ρ represents the tissue density and E represents the Young's modulus value of the tissue. Under certain conditions, a greater Young's modulus means greater tissue stiffness.
Further, from the propagation velocity values of the shear wave at the respective positions, the shear modulus, the propagation distance in a certain fixed time, the average propagation velocity in the target region, and the like can be further calculated.
And step S104, imaging and displaying the result of the shear wave parameter calculation.
After the final propagation velocity data is obtained, the propagation velocity data can be displayed on an image to form a propagation velocity distribution graph, and the propagation velocity difference between positions on the graph directly reflects the hardness difference. Of course, other parameter maps may be displayed, such as a young's modulus parameter map, a shear modulus parameter map, a propagation distance parameter map over a certain period of time, an average velocity value parameter map within a target region, and the like. The parameters can be processed and displayed into a movie picture, a plane or space distribution picture, parameter values, a curve graph and the like, can also be subjected to gray scale or color coding, and can also be displayed together with other mode pictures such as an anatomical picture after being superposed or fused.
As shown in fig. 9, the present invention further provides a shear wave imaging system, which includes an ultrasonic probe 11, acontrol module 12, asignal processing module 13, acomputing module 15, and adisplay system 17, where the ultrasonic probe 11 is provided with atransceiver module 110, thesignal processing module 13, thecomputing module 15, and thedisplay system 17 of the ultrasonic probe 11 are sequentially connected, and thecontrol module 12 is connected to thetransceiver module 110. Wherein:
thetransceiver module 110 is configured to transmit a tracking pulse and receive echo data of the tracking pulse and the reference pulse.
Thecontrol module 12 is configured to control thetransceiver module 110 to transmit tracking pulses. In practical use, thecontrol module 12 transmits a specific ultrasonic sequence of tracking pulses at preset time intervals, so as to trace shear waves and provide thetransceiver module 110 of the ultrasonic probe 11 with receiving corresponding echo data.
Thesignal processing module 13 is used for performing signal preprocessing on the echo data, so as to facilitate the subsequent calculation by the calculatingmodule 15, where the signal preprocessing may include beam forming processing, and may further include signal amplification, analog-to-digital conversion, quadrature decomposition, and the like.
Thecomputation module 15 is used for estimating the positions of the shear waves at different time instants, and for performing processing computation on the signals output by the beam synthesis.
In this embodiment, the calculatingmodule 15 includes:
theestimating unit 151 is configured to estimate estimated positions of the shear wave at various times according to a propagation duration of the shear wave and an average speed of the shear wave propagating in the target tissue.
And a data calculating unit 153 for calculating propagation parameters of the shear wave.
Thedisplay system 17 is configured to display an image of the calculation result of the shear wave parameters generated by thecalculation module 15.
It can be understood that the physical arrangement positions of the ultrasonic probe 11, thecontrol module 12, thesignal processing module 13, thecalculation module 15 and thedisplay system 17 can be adjusted by themselves according to the needs, for example, the ultrasonic probe 11, thecontrol module 12, thesignal processing module 13, thecalculation module 15 and thedisplay system 17 can be uniformly arranged in the same shell, so as to realize integral arrangement; or the device can be arranged separately and connected in a wired or wireless mode to carry out data communication.
The shear wave imaging method and the shear wave imaging system provided by the invention generate shear waves in tissues, estimate and track the propagation process of the shear waves within a period of time, and track the propagation position continuously, so that the propagation position information of the shear waves is acquired in a small range at each moment, the acquired information is integrated, elasticity-related parameters such as a shear wave wavefront electrogram, a propagation distance and a propagation speed in a target area are calculated, and finally imaging is carried out to reflect the elasticity difference among different tissues. The shear wave imaging method of the invention can accurately detect the shear wave in a small range due to the pre-estimated detection position of the shear wave, thereby relatively concentrating the detection energy and improving the detection signal-to-noise ratio. Meanwhile, the redundant detection times are reduced, the detection process is accelerated, and the data processing burden of the system is reduced.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.