Correction of phasefront aberrations and pulse reverberations in medical ultrasound imaging
First Claim
1. A method for corrections of phasefront aberrations and pulse reverberations in medical ultrasound imaging, whereultrasound beams on transmit and/or receive are formed with an ultrasound transducer array that has a two-dimensional distribution of elements, a maximal linear dimension of the elements being smaller than a spatial correlation length of the phase amplitude seen across the array surface, a individual array element signals are filtered in a correction filter before standard beam forming is done, both for the transmit and/or the receive beams, the correction filters are estimated byintroducing into a soft tissue image field one or more artificial ultrasound point scatterers, receiving backscatterd signal from the point scatterers with the transducer array, the point scatterers being spaced apart that the signals from the individual scatterers can clearly be discriminated from each other, the signals from the point scatterers having characteristics in amplitude or frequency content, or both, so that they are clearly separable from the tissue signal, the signals from the individual point scatterers being used to derive correction filters to correct for phase aberrations and pulse reverberations both in the receive and the transmit beams.
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Abstract
A method of correcting for phasefront aberrations in ultrasound imaging uses highly spaced apart point scatterers artificially placed in the tissue being imaged. The point scatterers reflect the transmitted sound and are individually differentiated to provide singular reference points for correction of signals reflected from the surrounding tissue. The differentiation is performed by comparison of the third or fourth harmonic frequencies of the reflected signals. To ensure the necessary high dispersal of the point scatterers, high amplitude pulses of the transmitted signal destroy point scatterers in selected image regions. In an alternate embodiment, correction is performed by stochastic analysis of signals reflected from the highly dispersed point scatterers. A reference signal is compared to the second harmonic of the reflected signal to reduce noise.
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Citations
43 Claims
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1. A method for corrections of phasefront aberrations and pulse reverberations in medical ultrasound imaging, where
ultrasound beams on transmit and/or receive are formed with an ultrasound transducer array that has a two-dimensional distribution of elements, a maximal linear dimension of the elements being smaller than a spatial correlation length of the phase amplitude seen across the array surface, a individual array element signals are filtered in a correction filter before standard beam forming is done, both for the transmit and/or the receive beams, the correction filters are estimated by introducing into a soft tissue image field one or more artificial ultrasound point scatterers, receiving backscatterd signal from the point scatterers with the transducer array, the point scatterers being spaced apart that the signals from the individual scatterers can clearly be discriminated from each other, the signals from the point scatterers having characteristics in amplitude or frequency content, or both, so that they are clearly separable from the tissue signal, the signals from the individual point scatterers being used to derive correction filters to correct for phase aberrations and pulse reverberations both in the receive and the transmit beams.
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15. A method for corrections of phasefront aberrations and pulse reverberations in medical ultrasound imaging, where
the ultrasound beams on transmit and/or receive are formed with an ultrasound transducer array that has a two-dimensional distribution of elements, a maximal linear dimension of the elements being smaller than a spatial correlation length of the phase amplitude seen across the array surface, individual array element signals being filtered in correction filters before standard beam forming is done, both for the transmit and/or the receive beams, the correction filters being estimated from the received element signals from the array elements back scattered from a distribution of scatterers with short correlation length, using an estimation algorithm for the correction filters that reduces the effect of pulse reverberations in the backscattered signal in a final estimate of correction filters.
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