Method and device for ultrasound imaging
View Patent ↗A method of high-resolution ultrasound imaging, in which transducers are made to emit ultrasound waves in a field of observations containing micro bubbles, by making the micro bubbles burst one by one in tandem with the emissions of ultrasound waves. At each shot j of an ultrasound wave, raw reverberated signals S j (i,t) picked up by each transducer i are recorded, and then differential signals V j (i,t) representative of variations between successive raw signals are determined, a parabolic function P j (x) is fitted to the differential signals corresponding to each shot j, and then a crest A j (x 0 ,y 0 ) of this function P j , corresponding to the position of the micro bubble destroyed between shots j−1 and j, is determined.
1. An ultrasound imaging method for imaging a field of observation in an environment to be imaged containing scatterers, said method comprising several successive measurement steps during each of which:
an array of transducers emits an incident ultrasound wave into the field of observation, of center wavelength λ,
then raw signals Sj(i,t) picked up by each transducer and representative of a reflected ultrasound wave reverberated from the incident wave by the scatterers in the environment are recorded, i being an index denoting each transducer, j being an index denoting each measurement step, and t denoting the time,
the array of transducers extending along at least one dimension and the incident waves mainly being propagated in a direction of propagation perpendicular to the array of transducers,
wherein a maximum number C of differential targets is generated, differing from one measurement step to another, each differential target being a scatterer which is present in the field of observation during a measurement step and absent during an immediately adjacent measurement step,
the number C being at most equal to INT(A/(5λ) 2 )+1, where A is an area of the field of observation,
and wherein said method further comprises the following steps:
a differential processing step during which the raw signals Sj(i,t) corresponding to successive measurement steps of index j are compared in order to extract differential signals Vj(i,t) representative of variations between raw signals from the successive measurement steps,
an adjustment step during which at least one function y=Pj(x) corresponding to each differential signal Vj(i,t) is determined, where x is a space variable denoting a position perpendicular to the direction of propagation and y is a coordinate denoting the position of a point along the direction of propagation corresponding to a travel time t,
and a positioning step during which a crest Aj(x0,y0) of said function Pj is determined, corresponding to the position of the differential target.
2. The method according to claim 1 , wherein the number C is at most equal to 2, preferably being equal to 1.
3. The method according to claim 1 , wherein, during the adjustment step, the function y=Pj(x) is determined by adjusting said function to minimize deviations with points Dj(xi,yi), where xi is a space variable denoting a position of each transducer i perpendicularly to the direction of propagation and yi is a coordinate denoting the position of a point along the direction of propagation corresponding to a travel time ti characteristic of the signal Vj(i,t).
4. The method according to claim 1 , wherein said function P is parabolic.
5. The method according to claim 1 , wherein the differential processing step comprises a sub-step of calculating raw differential signals, during which raw differential signals Vbj(i,t)=Sj(i,t)−Sj−1(i,t) are determined.
6. The method according to claim 1 , wherein the differential processing step comprises a sub-step of calculating raw differential signals, during which raw differential signals Vbj(i,t) are determined at least by a high-pass filtering of raw signals Sj(i,t) on j.
7. The method according to claim 5 , wherein the differential processing step further comprises a sub-step of determining an envelope, during which the differential signals Vj(i,t) are determined by calculating a temporal envelope of each raw differential signal Vbj(i,t).
8. The method according to claim 7 , wherein the sub-step of determining an envelope comprises a calculation of a temporal envelope Vej(i,t) then a low-pass filtering of the temporal envelopes Vej(i,t) on i in order to obtain the differential signals Vj(i,t).
9. The method according to claim 1 , wherein the field of observation comprises micro bubbles and the micro bubbles which have disappeared from the field of observation from one measurement step to another are detected, these micro bubbles that have disappeared constituting said differential targets.
10. The method according to claim 9 , wherein the incident wave has an amplitude suitable for destroying the maximum number C of micro bubbles in each measurement step.
11. The method according to claim 9 , wherein the incident wave emitted in each measurement step has an amplitude suitable for not destroying micro bubbles, and the method further comprises, alternating with the measurement steps, destruction steps during which a destructive ultrasound wave is emitted that has an amplitude suitable for destroying the maximum number C of micro bubbles in each destruction step.
12. The method according to claim 1 , wherein the positions Aj(x0,y0) of the successive differential targets are plotted on an image of the field of observation.
13. The method according to claim 12 , wherein said image of the field of observation is obtained by ultrasonography using said array of transducers.
14. An ultrasound imaging device comprising an array of transducers controlled by a control and processing device adapted for imaging a field of observation in an environment to be imaged containing scatterers,
the control and processing device being adapted for, during a plurality of successive measurement steps:
causing the array of transducers to emit an incident ultrasound wave into the field of observation in each measurement step,
then recording raw signals Sj(i,t) picked up by each transducer and representative of a reflected ultrasound wave reverberated from the incident wave by the scatterers of the environment, i being an index denoting each transducer, j being an index denoting each measurement step, and t denoting the time,
the array of transducers extending along at least one dimension and the incident waves mainly propagating in a direction of propagation perpendicular to the array of transducers,
wherein the control and processing device is adopted to generate a maximum number C of differential targets, differing from one measurement step to another, each differential target being a scatterer which is present in the field of observation during a measurement step and absent during an immediately adjacent measurement step,
the number C being at most equal to INT(A/(5λ) 2 )+1, where A is an area of the field of observation,
and wherein the control and processing device is further adopted to further carry out the following steps:
a differential processing step during which the raw signals Sj(i,t) corresponding to successive measurement steps of index j are compared in order to extract differential signals Vj(i,t) representative of variations between raw signals from the successive measurement steps,
an adjustment step during which at least one function y=Pj(x) corresponding to each differential signal Vj(i,t) is determined, where x is a space variable denoting a position perpendicular to the direction of propagation and y is a coordinate denoting the position of a point along the direction of propagation corresponding to a travel time t,
and a positioning step during which a crest Aj(x0,y0) of said function Pj is determined, corresponding to the position of the differential target.