Abstract:

BACKGROUND: The imaging mechanism of MRI means there is a contradiction between the time/space resolution and signal noise ratio (SNR). Thus, the image denoising becomes very necessary. The image denoising method using discrete wavelet transform (DWT) has been applied widely. However, DWT has some drawbacks. The drawbacks of DWT have led to the development of shift insensitive wavelet transforms, e.g. Kingsbury’s double-tree complex wavelet transform (DTCWT), which necessarily leads to considerably redundant wavelet representation and a huge increase in computational complexity.
OBJECTIVE: To design wavelet filter to reduce influence in sampling and maintain non-redundancy of DTCWT and analyze denoising of Rician noise of MRI images.
METHODS: The shift sensitivity was mainly caused by the aliasing terms in the downsampling of wavelet decomposition. A new scheme was proposed to approximately eliminate the aliasing terms while remains the wavelet representation free from redundancy. The framework of the proposed DWT was similar to that of the general DWT except that the wavelet filters satisfy some additional requirements beyond the requirements on wavelet filters. A biorthogonal wavelet was designed. The proposed wavelet was applied to denoise the magnetic resonance image with Rician noise using general the thresholding method.
RESULTS AND CONCLUSION: A new method for designing wavelet filter, which simplifies the design procedures into an optimal procedure with constraint conditions. The designed biorthogonal wavelet was used in MR images. The simulation results show the superiority of the proposed wavelet in the term of SNR.