T2 RESTORATION AND NOISE SUPPRESSION OF HYBRID MR-IMAGES USING WIENERAND LINEAR PREDICTION TECHNIQUES

This paper addresses the problem of enhancing hybrid magnetic resonanc e (MR) images degraded by T2 effects and additive measurement noise. T o reduce imaging time, MR signals are acquired using hybrid imaging (H I) sequences such as rapid acquisition relaxation-enhanced (RARE) and fast spin-echo (FSE). With these techniques, T2 effects act as a disto rtion filter. This T2 filter affects the signal and results in image s patial resolution and/or contrast loss. Furthermore, the amplitude ant i phase discontinuities in the T2 filter frequency response function m ay generate serious ringing artifacts. These distortions will damage i mage quality and affect object detectability. We use the Wiener filter and linear prediction (LP) technique to process HI MR signals in the spatial frequency domain (K-space) and the hybrid domain, respectively . Based on the average amplitude symmetry constraint of the spin echo signal, the amplitude frequency response function of the T2 distortion filter can be estimated and used in the Wiener filter for a global T2 amplitude restoration. Then, the linear prediction technique is utili zed to obtain the local signal amplitude and phase estimates around th e discontinuities of the frequency response function of the T2 filter. These estimates are used to make local amplitude and phase correction s, The effectiveness of this combined technique in correcting T2 disto rtion and reducing the measurement noise is analyzed and demonstrated using experiments on both phantoms and human studies.