MT Effects and T1 Quantification in Single-slice Spoiled Gradient Echo Imaging

We investigated magnetization transfer (MT) effects on the steady-state MR signal for a sample subjected to a series of identical on-resonance RF pulses, such as would be experienced while imaging a single slice using a spoiled gradient echo sequence. The MT coupling terms for a two-pool system were added to the Bloch equations and we derived the resulting steady-state signal equation and compared this result to the conventional signal equation without MT effects. The steady-state signal is increased by a few percent of the equilibrium magnetization because of MT. One consequence of this MT effect is inaccuracy in T(1) values determined via conventional steady-state gradient echo methods. (Theory predicts greater than 10% errors in T(1) for white matter when using short TR.) A second consequence is the ability to quantify the relaxation and MT parameters by fitting the gradient echo steady state signal to the signal equation appropriately modified to include MT effects. The theory was tested in samples of MnCl(2), cross-linked bovine serum albumin (BSA), and cross-linked BSA + MnCl(2).