T2′ mapping of the brain from water-unsuppressed ¹H-MRSI and turbo spin-echo data

Purpose: To obtain high-quality (Formula presented.) maps of brain tissues from water-unsuppressed magnetic resonance spectroscopic imaging (MRSI) and turbo spin-echo (TSE) data. Methods: (Formula presented.) mapping can be achieved using (Formula presented.) mapping from water-unsuppressed MRSI data and (Formula presented.) mapping from TSE data. However, (Formula presented.) mapping often suffers from signal dephasing and distortions caused by (Formula presented.) field inhomogeneity; (Formula presented.) measurements may be biased due to system imperfections, especially for (Formula presented.) -weighted image with small number of TEs. In this work, we corrected the (Formula presented.) field inhomogeneity effect on (Formula presented.) mapping using a subspace model-based method, incorporating pre-learned spectral basis functions of the water signals. (Formula presented.) estimation bias was corrected using a TE-adjustment method, which modeled the deviation between measured and reference (Formula presented.) decays as TE shifts. Results: In vivo experiments were performed to evaluate the performance of the proposed method. High-quality (Formula presented.) maps were obtained in the presence of large field inhomogeneity in the prefrontal cortex. Bias in (Formula presented.) measurements obtained from TSE data was effectively reduced. Based on the (Formula presented.) and (Formula presented.) measurements produced by the proposed method, high-quality (Formula presented.) 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. Conclusions: High-quality (Formula presented.) 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.