Musculoskeletal MR imaging at 4 T and at 1.5 T: comparison of relaxation times and image contrast.

Abstract

To evaluate the relaxation time-based contrast between the main tissues of the musculoskeletal system as measured in the human knee with magnetic resonance imaging at 4 T and 1.5 T. Five volunteers underwent 4-T and 1.5-T imaging. Inversion-recovery series were used to measure T1 values, and T2 values were measured with a spin-echo sequence. T1 values increased in all tissues with 4-T imaging. Values increased in muscle from 1 to 1.8 seconds, in fat from 0.3 to 0.4 seconds, and in cartilage from 0.8 to 1.5 seconds. T2 values were 10%-20% shorter in all tissues at 4 T. Advantages of 4-T imaging compared with 1.5-T imaging include a higher signal-to-noise ratio and an improved signal difference-to-noise ratio. However, any improvement in signal-to-noise ratio at high field strengths can partially be reduced by the increase in the T1 value. The slightly shorter T2 values at 4 T do not affect image contrast.