Signal to Noise Ratio and Uncertainty in Diffusion Tensor Imaging at 1.5, 3.0, and 7.0 Tesla

Purpose: To compare diffusion tensor imaging (DTI) measurements at ultra high field strength (7 Tesla [T]) in human volunteers with DTI measurements performed at 1.5 and 3 Tesla. Materials and Methods: The signal to noise ratio (SNR) and the uncertainty in fitted DTI parameters fractional anisotropy and primary eigenvector are assessed with tractography based regions of interest, measured in nine volunteers at 1.5T, 3T, and 7T with clinically available hardware configurations. Results: An increase in SNR is observed on the 7T system compared with the 1.5 or 3T system. The measured increase in SNR at 7T is larger than expected from field strength alone, indicating the large influence of improved receive coil hardware. Additionally, while the average fractional anisotropy remains relatively constant across field strengths, a decrease in uncertainty in the fitted values for fractional anisotropy and the principal eigenvector of the DTI tensor was found. Increased spatial heterogeneity of signal intensities is observed at 7T. Conclusion: Given the current hardware constraints, DTI at ultra-high field strengths is possible with improved performance in selected regions of interest.