Optimization of the ultrafast Look-Locker echo-planar imaging T1 mapping sequence.

The Look-Locker echo-planar imaging (LL-EPI) sequence has been numerically optimized in terms of the signal-to-noise ratio in the measured value of T1, for both single-shot (repetition time (TR) = infinity), and dynamically repeated T1 measurements. The sequence is optimized for the normal biologic range of T1 (0.2 s to 2.0 s) and for a range of sequence parameters found on most magnetic resonance (MR) scanners. Both linearly and geometrically spaced magnetization sample pulse intervals were considered. For single-shot measurements, the sequence with 24 linearly spaced sample pulses, an inversion time of 0.01 s, an inter-sample pulse delay of 0.10 s, and a sample radiofrequency (RF) pulse flip angle of 25 degrees was found to be optimum. When the number of sample pulses was limited due to hardware limitations, different pulse sequence parameters were indicated. The optimization procedures used are appropriate for any single-shot T1 mapping sequence variant and for any rapid T1 mapping application. The use of an optimized Look-Locker echo-planar imaging sequence is demonstrated by an example of dynamic contrast-enhanced scanning in the brain using fast T1 mapping.

[1]  M O Leach,et al.  A simple method for the restoration of signal polarity in multi‐image inversion recovery sequences for measuring T1 , 1991, Magnetic resonance in medicine.

[2]  A. Crawley,et al.  A comparison of one‐shot and recovery methods in T1 imaging , 1988, Magnetic resonance in medicine.

[3]  D. Look,et al.  Time Saving in Measurement of NMR and EPR Relaxation Times , 1970 .

[4]  R. Henkelman,et al.  Practical Implementation and Optimization of One‐shot T1 imaging , 1991, Magnetic resonance in medicine.

[5]  P. Tofts,et al.  Measurement of the blood‐brain barrier permeability and leakage space using dynamic MR imaging. 1. Fundamental concepts , 1991, Magnetic resonance in medicine.

[6]  William H. Press,et al.  Numerical recipes in C. The art of scientific computing , 1987 .

[7]  M. S. Silver,et al.  Highly selective {π}/{2} and π pulse generation , 1984 .

[8]  R. Bowtell,et al.  In vivo relaxation time measurements in the human placenta using echo planar imaging at 0.5 T. , 1998, Magnetic resonance imaging.

[9]  R. Henkelman.  Measurement of signal intensities in the presence of noise in MR images. , 1985, Medical physics.

[10]  P. Gowland,et al.  Accurate measurement of T1 in vivo in less than 3 seconds using echo‐planar imaging , 1993, Magnetic resonance in medicine.

[11]  P. Gowland,et al.  Dynamic studies of gadolinium uptake in brain tumors using inversion‐recovery echo‐planar imaging , 1992, Magnetic resonance in medicine.