An improved 3-D Look--Locker imaging method for T(1) parameter estimation.

The 3-D Look-Locker (LL) imaging method has been shown to be a highly efficient and accurate method for the volumetric mapping of the spin lattice relaxation time T(1). However, conventional 3-D LL imaging schemes are typically limited to small tip angle RF pulses (<or=5 degrees ) due to the large number of pulses required for adequate phase encoding and sampling of the recovery curve, which would otherwise drive the magnetization to steady state too rapidly, hence, diminishing the signal-to-noise ratio (SNR) available for accurate T(1) estimation. In this work, a more generalized form of the 3-D LL imaging method that incorporates an additional and variable delay time between recovery samples is described, which permits the use of larger tip angles (>5 degrees ), thereby improving the SNR and the accuracy of the method. In phantom studies, a mean T(1) measurement accuracy of less than 2% (0.2-3.1%) using a tip angle of 10 degrees was obtained for a range of T(1) from approximately 300 to 1,700 ms with a measurement time increase of only 15%. This accuracy compares favorably with the conventional 3-D LL method that provided an accuracy between 2.2% and 7.3% using a 5 degrees flip angle.