Method for imaging a sample with blood and associated devices
The present invention aims at improving the Doppler imaging of a biological sample comprising blood. For this, it is proposed a method for imaging a biological sample ( 10 ), the sample ( 10 ) comprising blood ( 14 ) comprising diffusors and solid tissue ( 16 ), the method comprising obtaining observation, each observation being characterized by a different point spread function associating a signal to each location of the region of interest, the signal comprising a first contribution representative of the diffusors of blood vessels within the location, a second contribution representative of the tissue diffusors and a third contribution representative of blood signal associated to blood diffusors outside of the location, and estimating, for each location, the blood flow by using a statistical analysis.
1. A method for imaging a biological sample, the sample comprising diffusors of blood vessels and solid tissue, the method comprising:
an imaging step comprising the following operations:
an emitting operation in which unfocused ultrasound waves in a region of interest are emitted during a time interval, the ratio of the number of unfocused ultrasound waves over the time interval being superior or equal to 100 unfocused ultrasound waves per second,
a collecting operation in which retroreflected waves from the diffusors of the region of interest are collected, and
an image formation operation in which different observations of the region of interest are generated based on the collected retroreflected waves, each observation being characterized by a different and partially spatially decorrelated point spread function associating a blood flow signal to each location of the region of interest, the blood flow signal comprising a first contribution representative of the diffusors of blood vessels within the location, a second contribution representative of tissue diffusors, and a third contribution representative of blood diffusors outside of the location, wherein the second and third contribution are undesired,
the imaging step being iterated M times to obtain observation sets of M temporal realizations of the region of interest, M being superior or equal to 10,
a filtering step for reducing the second contribution of each of the observation sets, and
an estimating step in which, for each location of the region of interest, the blood flow signal is estimated, the estimating step comprising the following operations:
applying a statistical analysis operation on each observation set to discriminate the first contribution and the third contribution by the use of the spatial decorrelation of blood signals originating from distinct locations through the statistical analysis operation based on the joint variability of the observations of each set, and
calculating an estimate of a component of the blood flow signal based on the first contribution.
2. The method according to claim 1 , wherein the emitting and collecting operations are carried out by using a row-column array of ultrasound transducers.
3. The method according to claim 1 , wherein the ratio of the number of unfocused ultrasound waves over the time interval is superior or equal to 500 unfocused ultrasound waves per second.
4. The method according to claim 1 , wherein the number of observations is the same for each set of observations.
5. The method according to claim 1 , wherein the number of observations is equal to 2.
6. The method according to claim 1 , wherein the emitting and collecting operations are carried out by using an array of ultrasound transducers, the array of ultrasound transducers being one of a one-dimensional array, a two-dimensional array, or a sparse array.
7. The method according to claim 1 , wherein the emitting and collecting operations are carried out by using two orthogonal arrays of ultrasound transducers.
8. The method according to claim 1 , wherein, at the operation of applying, the statistical analysis is chosen among a principal component analysis, a singular value decomposition and an independent component analysis.
9. The method according to claim 1 , wherein the operation of applying the statistical analysis comprises estimating the conjugated product between pairs of observations.
10. The method according to claim 1 , wherein the operation of applying the statistical analysis comprises calculating an estimate of the covariance of the observations.
11. The method according to claim 1 , wherein the integer M is superior or equal to 20.
12. The method according to claim 1 , wherein the emitting and collecting operations are carried out by using an array of ultrasound transducers adapted to electronically focus in reception along two preferential directions.
13. The method according to claim 1 , wherein the imaging step uses blood scatterers that are acoustic contrast agents.
14. An imaging device for imaging a biological sample, the sample comprising diffusors of blood vessels and solid tissue, the imaging device comprising an ultrasound imager adapted to carry out an imaging step comprising the following operations:
an emitting operation in which unfocused ultrasound waves in a region of interest are emitted during a time interval, the ratio of the number of unfocused ultrasound waves over the time interval being superior or equal to 100 unfocused ultrasound waves per second,
a collecting operation in which retroreflected waves from the diffusors of the region of interest are collected, and
an image formation operation in which different observations of the region of interest are generated based on the collected retroreflected waves, each observation being characterized by a different and partially spatially decorrelated point spread function associating a blood flow signal to each location of the region of interest, the blood flow signal comprising a first contribution representative of the diffusors of blood vessels within the location, a second contribution representative of tissue diffusors, and a third contribution representative of blood diffusors outside of the location, wherein the second and third contribution are undesired,
the imaging step being iterated M times to obtain observation sets of M temporal realizations of the region of interest, M being superior or equal to 10,
the imaging device further comprising a calculator adapted to carry out:
a filtering step for reducing the second contribution of each of the observation sets, and
an estimating step in which, for each location of the region of interest, the blood flow signal is estimated, the estimating step comprising the following operations:
applying a statistical analysis operation on each observation set to discriminate the first contribution and the third contribution by the use of the spatial decorrelation of blood signals originating from distinct locations through the statistical analysis operation based on the joint variability of the observations of each set, and
calculating an estimate of a component of the blood flow signal based on the first contribution.
15. A non-transitory computer readable medium encoded with instructions executable by a computer for controlling an ultrasound imager to carry out imaging having the following operations:
an emitting operation in which unfocused ultrasound waves in the region of interest are emitted during a time interval, the ratio of the number of unfocused ultrasound waves over the time interval being superior or equal to 100 unfocused ultrasound waves per second,
a collecting operation in which retroreflected waves from the diffusors of the given region of interest are collected, and
an image formation operation in which different observations of the region of interest are generated based on the collected retroreflected waves, each observation being characterized by a different and partially spatially decorrelated point spread function associating a blood flow signal to each location of the region of interest, the blood flow signal comprising a first contribution representative of the diffusors of blood vessels within the location, a second contribution representative of tissue diffusors, and a third contribution representative of blood diffusors outside of the location, wherein the second and third contribution are undesired,
the imaging device further comprising a calculator controlled by the instructions encoded on the nontransitory computer readable medium to carry out:
a filtering step for reducing the second contribution of each of the observation sets, and
an estimating step in which, for each location of the region of interest, the blood flow signal is estimated, the estimating step comprising the following operations:
applying a statistical analysis operation on each observation set to discriminate the first contribution and the third contribution by the use of the spatial decorrelation of blood signals originating from distinct locations through the statistical analysis operation based on the joint variability of the observations of each set, and
calculating an estimate of a component of the blood flow signal based on the first contribution.