Relaxation by amplitude modulation: A rapid T 1 measurement method

Purpose A novel longitudinal relaxation time ( T 1 ) measurement method using complex amplitude modulation is presented. Theory The method applies a series of inversion pulses to the imaged region in accordance with a binary modulation sequence. The longitudinal magnetization acquired in a given pulse repetition time ( TR ) interval is the sum of the individual longitudinal magnetization recovered during each previous TR interval, weighted by T 1 decay factors and the combined effect of all the radiofrequency pulses they have experienced. The demodulated signal for each voxel is an exponential curve with a decaying rate determined by T 1 and the acquisition flip angle θ. Methods Sequences using a 15‐cycle pseudorandom binary code were implemented on Siemens 3T Trio with standard gradient echo readout and multislice gradient echo‐planar imaging. The sequences were tested on T 1 phantoms and human and compared against inversion recovery method. Results Our studies on phantoms and a human volunteer show that T 1 estimated from this method is very accurate and well reproducible. The average scan time is ∼1.6 s per slice (full k‐space gradient echo‐planar imaging with matrix size 128 × 128). Conclusion The current protocol is almost twice as fast as two fastest existing methods. Optimizing protocols and incorporating common acceleration techniques will make it even faster. Magn Reson Med 71:2155–2165, 2014. © 2013 Wiley Periodicals, Inc.