On- and off-resonance spin-lock MR imaging of normal human brain at 0.1 T: possibilities to modify image contrast

Abstract

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T 1ρ) and off-resonance spin lock relaxation parameters (T 1ρ off, M e/M o), MT parameters (T 1sat, M s/M o), and T 1, T 2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T 1ρ for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 μT to 250 μT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 μT, T 1ρ off for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B eff) and the z-axis (θ) ranging from 60° to 15°, respectively. The T 1ρ of the white and gray matters increased significantly with increasing locking field amplitude ( p < 0.001). The T 1ρ off decreased significantly with increasing θ ( p < 0.001). T 1ρ and T 1ρ off with θ ≥ 30° were statistically significantly shorter in the frontal than in the parietal white matters ( p < 0.05). The duration, amplitude and θ of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.