T1 and T2 quantification from standard turbo spin echo images

Purpose: To extract longitudinal and transverse (T-1 and T-2) relaxation maps from standard MRI methods. Methods: Bloch simulations were used to model relative signal amplitudes from standard turbo spin-echo sequences: proton density weighted, T-2-weighted, and either T-2-weighted fluid attenuated inversion recovery or T-1-weighted images. Simulations over a range of expected parameter values yielded a look-up table of relative signal intensities of these sequences. Weighted images and flip angle maps were acquired in 8 subjects at 3 T using both single and multislice acquisitions. The T-1 and T-2 maps were fit by comparing the weighted images to the look-up table, given the measured flip angles. Results were compared with inversion recovery and multi-echo spin-echo experiments. Results: A region analysis showed that relaxation maps computed from single-slice proton density, T-2 and T-1 weighting provided a mean T-1 error of 4% in gray matter and 11% in white matter, and a mean T-2 error of 3% and 4%, respectively, in comparison to reference measurements. In multislice acquisitions that are optimized to reduce cross-talk and incidental magnetization transfer, the mean T-1 error was 7% in gray matter and 1% in white matter, and the mean T-2 errors were 3% and 4%, respectively. The best T-1 results were achieved using proton density, T-2 and T-1 weighting rather than the fluid attenuated inversion recovery, although T-2 maps were largely unaffected by this choice. Incidental magnetization transfer reduced T-1 accuracy in standard interleaved multislice acquisitions. Conclusion: Through exact sequence modeling and separate flip angle measurement, T-2 and T-1 may be quantified from a turbo spin-echo brain protocol with proton density, T-2, and T-1 weighting.