Measuring T2 and T1, and imaging T2 without spin echoes

During adiabatic excitation, the nuclear magnetization in the transverse plane is subject to T-2 (spin-spin) relaxation, depending on the pulse length tau. Here, this property is exploited in a method of measuring T-2 using the ratio of NMR signals acquired with short and long-duration self-refocusing adiabatic pulses, without spin-echoes. This Dual-tau method is implemented with B-1-insensitive rotation (BIR-4) pulses. It is validated theoretically with Bloch equation simulations independent of flip-angle, and experimentally in phantoms. Dual-tau T-2 measurements are most accurate at short T-2 where results agree with standard spin-echo measures to within 10% for T-2 <= 100 ms. Dual-tau MRI performed with a long 0 degrees BIR-4 pre-pulse provides quantitative T-2 imaging of phantoms and the human foot while preserving desired contrast and functional properties of the rest of the MRI sequence. A single 0 degrees BIR-4 pre-pulse can provide T-2 contrast-weighted MRI and serve as a T-2-prep sequence with a lower B-1 requirement than prior approaches. Finally, a Tri-tau experiment is introduced in which both tau and flip-angle are varied, enabling measurement of T-2, T-1 and signal intensity in just three acquisitions if flip-angles are well-characterized. These new methods can potentially save time and simplify relaxation measurements and/or contrast-weighted NMR and MRI. (C) 2011 Elsevier Inc. All rights reserved.