## Feng Liu* and Shuangbao Ma**## |

NMRL | Median filtering | Soft threshold filtering | Hard threshold filtering | Improved algorithm |

SNR=10 | 13.15 | 10.34 | 10.45 | 27.57 |

SNR=20 | 22.85 | 20.18 | 20.28 | 32.38 |

SNR=30 | 32.77 | 30.21 | 30.29 | 34.71 |

Table 2.

NMRL | Median filtering | Soft threshold filtering | Hard threshold filtering | Improved algorithm |

SNR=1 | 1.5197 | 2.0642 | 2.0397 | 0.2833 |

SNR=2 | 0.4822 | 0.6561 | 0.6487 | 0.1523 |

SNR=3 | 0.1566 | 0.2072 | 0.2005 | 0.1229 |

Magnetic resonance imaging without having to filter the SNR is low, so only the data simulation of SNR is less than 30. From Table 1, the four algorithms of SNR can be analyzed. This improved algorithm can improve the SNR. In the first row of Table 1, After using a median filter algorithm noise ratio was 13.15, After using two thresholds for wavelet transform method SNR in turn was 10.34, 10.45, improved algorithm for filtering the SNR of 27.57, greatly improving the filtered SNR. From the data in Table 1, another conclusion can be analyzed that two thresholds for wavelet transform filter effect there is little difference.

Compared with other algorithms, this improved algorithm of mean square error is minimal. Smaller the RMSE, reflecting the filtered signal closer to the original signal, to prove the validity of the algorithm. According to the compared results from TableS 1 and 2, this improved de-noising algorithm not only improve the SNR of NMR signal, but also can effectively filter out the random noise.

This article intended for low SNR of NMR signal presents a modified filtering algorithm based on wavelet transform, which is a combination of mean filter algorithm with improved wavelet threshold filtering algorithm. The concrete steps are designed to improve filtering algorithms, based on hard threshold and soft threshold proposed an improved threshold function. Construct 32 large porosity modeling, and NMR signals generated by this model used for simulation, using median filtering and wavelet soft-threshold filtering, wavelets hard and improved threshold filtering algorithms for numerical simulation, after comparison of the simulation results and analysis, comparing and calculated the noise ratio of filtered signal and RMSE, as well as three algorithms in NMR spin-echostring comparison are testimony to the effectiveness of the algorithm. As the result shows that this improved de-nosing algorithm is very suit to deal with the spin echo train in NMRL.

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