Rapid methods for concurrent measurement of the RF‐pulse flip angle and the longitudinal relaxation time

Abstract

Measuring both the flip angle (FA) and the longitudinal relaxation time T₁ is essential in quantitative and longitudinal studies because the signal amplitude is dependent on these quantities. Conventional methods can only measure one of them at a time and require long scan times. In this work, two mutually consistent methods are developed; each can acquire multislice data for determining both the FA and T₁ in a scan time about half the time needed for a conventional FA measurement. On the basis of a recent development of longitudinal-relaxation measurement (Hsu and Lowe, J Magn Reson 2004;169:270–278; Hsu and Glover, J Magn Reson 2006;181:98–106), one of the methods uses RF pulse trains of two FAs whereas the other uses pulse trains of different pulse spacing. When only the FA or T₁ is needed, the present methods can still be faster than conventional methods for the needed quantity. In benchmarking with a uniform-density sample, both methods generate precise T₁ values independent of the FA chosen (except at and near 90°). In the demonstration with three normal volunteers at 3 T, the T₁ values of frontal and occipital white matter, putamen, and caudate are compared; the T₁ values are in agreement with literature values and the intrasubject deviation is 0.2%–2.8%. Magn Reson Med, 61:1319–1325, 2009.