T2′ mapping of the brain from water-unsuppressed 1H-MRSI and turbo spin-echo data
To obtain high-quality T2’ maps of brain tissues from water-unsuppressed magnetic resonance spectroscopic imaging (MRSI) and turbo spin-echo (TSE) data.
T2’ mapping can be achieved using T2* mapping from water-unsuppressed MRSI data and T2 mapping from TSE data. However, T2* mapping often suffers from signal dephasing and distortions caused by B0 field inhomogeneity;T2 measurements may be biased due to system imperfections, especially for T2-weighted image with small number of TEs. In this work, we corrected the B0 field inhomogeneity effect on T2* mapping using a subspace model-based method, incorporating pre-learned spectral basis functions of the water signals. T2 estimation bias was corrected using a TE-adjustment method, which modeled the deviation between measured and referenceT2 decays as TE shifts.
In vivo experiments were performed to evaluate the performance of the proposed method. High-quality T2* maps were obtained in the presence of large field inhomogeneity in the prefrontal cortex. Bias in T2 measurements obtained from TSE data was effectively reduced. Based on the T2* and T2 measurements produced by the proposed method, high-quality T2’ maps were obtained, along with neurometabolite maps, from MRSI and TSE data that were acquired in about 9 min. The results obtained from acute stroke and glioma patients demonstrated the feasibility of the proposed method in the clinical setting.
High-quality T2’ maps can be obtained from water-unsuppressed 1H-MRSI and TSE data using the proposed method. With further development, this method may lay a foundation for simultaneously imaging oxygenation and neurometabolic alterations of brain disorders.