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 B 0 maps at 3T show enhanced off‐resonance effects close to the diaphragm and the ribs due to susceptibility differences. The average T   * 2from a voxel (20 × 4 × 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 T   * 2are 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. J. Magn. Reson. Imaging 2009;30:418–423. © 2009 Wiley‐Liss, Inc.