B sub(0) dependence of the on-resonance longitudinal relaxation time in the rotating frame (T sub(1 rho )) in protein phantoms and rat brain in vivo

• Published in: Magnetic resonance in medicine 2004-01, Vol.51 (1), p.4-8
• Main Authors: Maekelae, H I, De Vita, E, Groehn, OHJ, Kettunen, MI, Kavec, M, Lythgoe, M, Garwood, M, Ordidge, R, Kauppinen, R A
• Format: Article
• Language: English
• ISSN: 0740-3194
• DOI: 10.1002/mrm.10669

On-resonance longitudinal relaxation time in the rotating frame (T sub(1 rho )) 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 T sub(1 rho ) relaxation were assessed by determining relaxation rates (R sub(1 rho )) in both protein phantoms and in rat brain at 2.35, 4.7, and 9.4 T. Similar to transverse relaxation rate (R sub(2)), R sub(1 rho ) increased substantially with increasing magnetic field strength (B sub(0)). The B sub(0) dependence was more pronounced at weak spin-lock fields. In contrast to R sub(1 rho ), longitudinal relaxation rate (R sub(1)) decreased as a function of increasing B sub(0) field. The present data argue that dipole-dipole interaction forms only one pathway for T sub(1 rho ) relaxation and the contributions from other physicochemical factors need to be considered.