Golay codes are the most practical code in coded ultrasound imaging systems.But the trade-off for perfect range sidelobe cancellation is the requirement for two firings, thus resulting in motion-dependent decoding errors.In view of this, we propose a new scheme using the simultaneous emission of code pairs.The code pair is allocated to different elements of an aperture and transmitted simultaneously.The process of separating the code pair from the echo received is based on the orthogonality of the code pair.At last the autocorrelation functions of the individual Golay codes are added together.The simultaneous emission of code pairs instead of two firings recovers the frame rate loss, and eliminates the motion-dependent decoding error.Our theoretical analysis and simulations show that the scheme can be used to eliminate the tissue motion effects.
Water-fat separation is a particularly important problem for magnetic resonance imaging.Although many methods have been proposed,the reliability is still challenging.In this work,we have presented a method based on the combination of the branch-cut method and multigrid algorithm to get a more robust performance of water-fat separation.First,the branch-cut method is applied to identify residues,which violates the requirement that the interacting phase gradient around a closed path be zero.Residues and branches are marked to be zeros and filled to the weighting factor array.Then,the unwrapped phase array can be given by the multigrid algorithm.Finally,the Dixon method for water-fat separation is applied to the unwrapped phase array.Experiments for brain scanning on the 0.3T low field MRI system demonstrate the successful application of the proposed method.
Hong-jun Tian1,Si-ping Chen2,Tian-fu Wang2,Xian-fen Diao2,Chong-xun Zheng1 1.Key Laboratory of Biomedical Information Engineering of Education Ministry,Xi’an Jiaotong University,Xi’an 710049
The increase of frame rate,though with the potential in a coded ultrasound system,is generally concomitant with the simultaneous transmission of a number of apertures,and in consequence leads to increased cross-talks between different apertures.In view of this,a new coding scheme using staggering repetition interval was proposed.The transmitting signals were constructed by repeating the two(or more) modulated codes using staggering repetition interval,and then allocated to and transmitted simultaneously among different apertures.The decoding process was based on the subsection-matched filter under the assistance of different matched filters for different apertures.At last the outputs of subsection-matched filtering were added together.Staggering changed the positions of cross-correlation(CC) peaks from coinciding,which resulted in an effective reduction of CC.Our theoretical analysis and simulations showed that,the coding scheme can be used to reduce cross-talk,and a good cross-talk reduction will be achieved if the staggering delay is kept in an appropriate range.
