Susceptibility effects in hyperpolarized (3)He lung MRI at 1.5T and 3T.

Purpose: To compare susceptibility effects in hyperpolarized 3 He lung MRI at the clinically relevant field strengths of 1.5T and 3T. Materials and Methods: Susceptibility-related B-0 inhomogeneity was evaluated on a macroscopic scale by B-0 field mapping via phase difference. Subpixel susceptibility effects were quantified by mapping T-2*. Comparison was made between ventilation images obtained from the same volunteers at both field strengths. Results: The 130 maps at 3T show enhanced off-resonance effects close to the diaphragm and the ribs due to susceptibility differences. The average T-2* from a voxel (20 x 4 x 4) mm 3 was determined as T-2* = 27.8 msec +/- 1.2 msec at 1.5T compared to T-2* = 14.4 msec +/- 2.6 msec at 3T. In ventilation images the most prominent effect is increased signal attenuation close to the intrapulmonary blood vessels at higher B-0. Conclusion: Image homogeneity and T2* are lower at 3T due to increased B-0 inhomogeneity as a consequence of susceptibility differences. These findings indicate that 3 He imaging at 3T has no obvious benefit over imaging at 1.5T. as signal-to-noise ratio (SNR) was comparable for both fields in this work.