Bo Dependence of the On-Resonance Longitudinal Relaxation Time in the Rotating Frame (T1ρ) in Protein Phantoms and Rat Brain in Vivo

Abstract

On-resonance longitudinal relaxation time in the rotating frame (T 1ρ) has been shown to provide unique information during the early minutes of acute stroke. In the present study, the contributions of the different relaxation mechanisms to on-resonance (T1ρ), relaxation were assessed by determining relaxation rates (R1ρ) in both protein phantoms and in rat brain at 2.35, 4.7, and 9.4 T. Similar to transverse relaxation rate (R2), R1ρ increased substantially with increasing magnetic field strength (Bo). The Bo dependence was more pronounced at weak spin-lock fields. In contrast to R1ρ, longitudinal relaxation rate (R1) decreased as a function of increasing Bo field. The present data argue that dipole-dipole interaction forms only one pathway for T 1ρ, relaxation and the contributions from other physicochemical factors need to be considered. © 2003 Wiley-Liss, Inc.