Determination of T1ρ values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1ρ relaxation times for normal tissues were determined. Furthermore, T1ρ was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1ρ values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T1ρ relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T1ρ demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T1ρ values measured at locking field strength (B1L) of 35 μT were close to T2 values, the only exception being fat tissue, which showed T1ρ values much longer than T2 values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.