T₁ and T₂ quantification from standard turbo spin echo images

To extract longitudinal and transverse (T₁ and T₂ ) relaxation maps from standard MRI methods.

Bloch simulations were used to model relative signal amplitudes from standard turbo spin-echo sequences: proton density weighted, T₂ -weighted, and either T₂ -weighted fluid attenuated inversion recovery or T₁ -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 T₁ and T₂ 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.

A region analysis showed that relaxation maps computed from single-slice proton density, T₂ and T₁ weighting provided a mean T₁ error of 4% in gray matter and 11% in white matter, and a mean T₂ 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 T₁ error was 7% in gray matter and 1% in white matter, and the mean T₂ errors were 3% and 4%, respectively. The best T₁ results were achieved using proton density, T₂ and T₁ weighting rather than the fluid attenuated inversion recovery, although T₂ maps were largely unaffected by this choice. Incidental magnetization transfer reduced T₁ accuracy in standard interleaved multislice acquisitions.

Through exact sequence modeling and separate flip angle measurement, T₂ and T₁ may be quantified from a turbo spin-echo brain protocol with proton density, T₂ , and T₁ weighting.