T1 ρ-weighted MRI using a surface coil to transmit spin-lock pulses

Abstract

T 1 ρ -weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B 1 inhomogeneity. First, excitation with a spatially varying B 1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B 1 results in non-uniform T 1 ρ contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T 1 ρ -weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This “self-compensating” T 1 ρ -preparatory pulse sequence was analyzed and the effect of an inhomogeneous B 1 field was simulated using the Bloch equations. T 1 ρ -weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T 1 ρ -prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.