Self-gated bSSFP sequences to detect iron-labeled cancer cells and/or metastases in vivo in mouse liver at 7 Tesla

Abstract

Background To develop and evaluate three-dimensional (3D) self-gated balanced steady state free precession (bSSFP) imaging at high magnetic fields to track iron-labeled cells and metastases in murine abdomens. Methods Mice were injected intravenously with iron-labeled melanoma cells and imaged at 7 Tesla (T). Respiration peaks were identified using Free Induction Decay acquired immediately after the radiofrequency pulse. Respiration-corrupted k-space lines were deleted. Four images were acquired to reconstruct final images using the Sum-Of-Square technique. Image sharpness, metastasis contrast and iron-labeled cell detection with SG-bSSFP sequence (acquired with echo time [TE]=3 ms or TE=6 ms) were compared with standard methods (gradient echo (GRE) and RARE). Results After reconstruction, the 3D SG-bSSFP images were 75-80% sharper, free from banding (75% liver signal-to-noise ratio recovery) and respiratory motion (26-42% improvement in signal homogeneity) artifacts. Metastasis contrast was twice higher on SG-bSSFP with TE=3 ms than on RARE images. Iron-labeled cells and metastases were simultaneously detected on SG-bSSFP images with TE=6 ms, with similar void intensity and tumor contrast to GRE and RARE, respectively. Halving acquisition time preserved iron sensitivity and metastasis contrast, allowing for 3D abdomen imaging in 13 min (TE=3 ms) or 26 min (TE=6 ms). Conclusion Combining a self-gating technique with bSSFP sequences at 7T provides high-resolution 3D artifact-free abdominal images of small animals. J. Magn. Reson. Imaging 2015;41:1413-1421.