In vivo measurement of T1ρ dispersion in the human brain at 1.5 tesla

Purpose: To measure T-1rho relaxation times and TIP dispersion in the human brain in vivo. Materials and Methods: Magnetic resonance imaging (MRI) was performed on a 1.5-T GE Signa clinical scanner using the standard GE head coil. A fast spin-echo (FSE)-based T-1rho-weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio-frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)-mandated safety levels. Results: T-1rho-weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T-2-weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T-1rho values for white matter (WM), gray matter (GM), and CSF were 85 +/- 3, 99 +/- 1, and 637 +/- 78 msec, respectively, at a spin-locking field of 500 Hz. T-1rho is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T-2 values. T-1rho dispersion was observed between spin-locking frequencies 0 and 500 Hz. Conclusion: T-1rho-weighted MRI provides images of the brain with superb contrast and detail. T-1rho values measured in the different brain tissues will serve as useful baseline values for analysis of T-1rho changes associated with pathology.