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

Abstract

Purpose: To compare susceptibility effects in hyperpolarized 3He lung MRI at the clinically relevant field strengths of 1.5T and 3T. Materials and Methods: Susceptibility-related B0 inhomogeneity was evaluated on a macroscopic scale by B0 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 B0 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 B0. Conclusion: Image homogeneity and T*2 are lower at 3T due to increased B0 inhomogeneity as a consequence of susceptibility differences. These findings indicate that 3He 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. © 2009 Wiley-Liss, Inc.