Correction of errors caused by imperfect inversion pulses in MR imaging measurement of T1 relaxation times

Abstract

Spin-lattice ( T 1) relaxation times were measured by an inversion-recovery magnetic resonance imaging method with a slice-selective inversion pulse (SIP), a non-selective rectangular inversion pulse (RIP), or a B 1-insensitive adiabatic inversion pulse (AIP). Data analysis either assumed perfect inversion (two-parameter fit) or allowed for imperfect inversion (three-parameter fit). Imperfect inversion pulses caused low T 1 values in phantoms with a two-parameter fit, while three-parameter T 1 estimates were accurate over the range 430–2670 ms. A difference of ∼10% between two-parameter and three-parameter T 1 values in normal human brain tissue was attributed to B 1 inhomogeneity with the slice-selective inversion pulse and rectangular inversion pulse, to the slice profile with the slice-selective inversion pulse, and to T 2 effects for the adiabatic inversion pulse. Any T 1 method that relies on accurate flip angles may have a significant systematic error in vivo. Phantom accuracy does not ensure accuracy in vivo, because phantoms may have a more homogeneous B 1 field and a longer T 2 than do biological samples.