Fast and accurate T2 mapping using Bloch simulations and low-rank plus sparse matrix decomposition.

PURPOSE: MRI's T2 relaxation time is one of the key contrast mechanisms for clinical diagnosis and prognosis of pathologies. Mapping this relaxation time, however, involves extensive scan times, which are needed to collect quantitative data, thereby impeding its integration into clinical routine. This study employs a low-rank plus sparse (L + S) signal decomposition approach in order to reconstruct accurate T2-maps from highly undersampled multi-echo spin-echo (MESE) MRI data. METHODS: Two new algorithms are presented: the first uses standard L + S approach, where both L and S are iteratively updated. The second technique, dubbed SPArse and fixed RanK (SPARK), uses a fixed-rank L, under the assumption that most MESE information is found in the L component and that this rank can be pre-calculated. The utility of these new techniques is demonstrated on in vivo brain and calf data at x2 to x6 acceleration factors. RESULTS: Accelerated T2 maps showed improved accuracy compared to fully sampled ground truth maps, when using L + S and SPARK techniques vis-à-vis standard GRAPPA acceleration. CONCLUSION: SPARK provides accurate T2 maps with increased robustness to the selection of reconstruction parameters making it suitable to a wide range of applications and facilitating the use of quantitative T2 information in clinical settings.

Therapeutic N-Acetyl-Cysteine (Nac) Following Initiation of Maternal Inflammation Attenuates Long-Term Offspring Cerebral Injury, as Evident in Magnetic Resonance Imaging (MRI).

Maternal infection/inflammation may induce fetal inflammatory responses, which have been associated with long-term offspring cerebral injury. We previously demonstrated that prophylactic N-Acetyl-Cysteine (NAC), administered prior to and following maternal lipopolysaccharide (LPS), reduced offspring cerebral injury as evident on MRI. In the present study, we used MRI to examine the effect of therapeutic NAC following maternal LPS-induced inflammation on neonatal brain injury. Pregnant Sprague-Dawley dams (n = 6) at day 18 of gestation received either intraperitoneal injection of LPS or saline (Control) at time 0. Animals were randomized to receive intravenous injection (tail vein) of NAC or saline at time +30 min. Pups were delivered spontaneously and allowed to mature until postnatal day 25. Male offspring (6-8 per group) were examined by MRI and analyzed using voxel-based analysis. Diffusion Tensor Imaging (DTI), an advanced MRI technique, was performed and quantitative parameters extracted (mean and radial diffusivity) and used to assess white and gray matter brain injury. Offspring of LPS-treated dams exhibited significantly increased mean, axial and radial diffusivity (RD) levels in white and gray matter consistent with cerebral injury. In contrast, offspring of NAC-treated LPS PS dams demonstrated reduced mean, axial and RD levels in most regions; similar to the saline group. Maternal NAC treatment following maternal inflammation significantly influenced brain micro-structure integrity as demonstrated by MRI-DTI scans. These findings suggest that maternal NAC therapy may be effective in human pregnancies associated with maternal/fetal inflammation, such as preterm rupture of membranes and chorioamnionitis.