Quantitative T_1ρ and adiabatic Carr-Purcell T₂ magnetic resonance imaging of human occipital lobe at 4 T

The feasibility of performing quantitative T_1ρ MRI in human brain at 4 T is shown. T_1ρ values obtained from five volunteers were compared with T² and adiabatic Carr-Purcell (CP) T₂ values. Measured relaxation time constants increased in order from T ₂, CP-T₂, T_1ρ both in white and gray matter, demonstrating differential sensitivities of these methods to dipolar interactions and/or proton exchange and diffusion in local microscopic field gradients, which are so-called dynamic averaging (DA) processes. In occipital lobe, all relaxation time constants were found to be higher in white matter than in gray matter, demonstrating contrast denoted as an "inverse transverse relaxation contrast." This contrast persisted despite changing the delay between refocusing pulses or changing the magnitude of the spin-lock field strength, which suggests that it does not originate from DA, as might be induced by the presence of Fe, but rather is related to dipolar interactions in the brain tissue.