Artifact reduction in functional magnetic resonance imaging
Functional magnetic resonance imaging (fMRI) is a relatively new non-invasive technique for monitoring brain activity with great spatial and temporal precision. Blood-oxygen-level-dependent (BOLD) fMRI operates by detecting localized changes in magnetic field homogeneity that accompany changes in blood oxygenation. However, fMRI studies are prone to artifacts caused by blood flow, variations in NMR signal phase, and patient motion. A new method of MR imaging called partial presaturation (PSAT) was developed that allows fMRI studies to be performed with reduced sensitivity to blood flow. The method is more effective than previous techniques for eliminating blood flow effects. New techniques called k-space phase correction and k-space orthogonalization were developed to remove artifacts caused by unwanted phase variations and intra-image motion during fMRI studies. The methods are easily implemented in post-processing of fMRI data. A simple Fourier-domain image registration algorithm was also developed to correct for inter-image motion. The combination of these techniques significantly improves the sensitivity and specificity of human fMRI experiments.