Artifacts Correction With Navigator Echo In MRI

As a non-invasive medical imaging technology, Magnetic Resonance Imaging (MRI) has been widely used in the field of clinical diagnosis. Compared with conventional medical imaging technology, MRI has high soft tissue contrast and it can provide a wealth of diagnostic information. However, artifacts usually occur during MR Imaging, some affecting the diagnostic quality, while others may be confused with pathology. Therefore, reduction of artifacts in MRI has been one of the remaining difficulties. Here, we present two methods to correct the artifacts due to motion.1. The gradient echo sequence is a fundamental pulse sequence in MRI. However, it is very sensitive to those spatially and temporally varying frequency offsets. This study addressed the issue of local field fluctuations in brain induced by susceptibility changes during respiration. The technique acquires a one-dimensional navigator signal before the application of the phase-encoding gradients and corrects the phase of the subsequently acquired imaging data in3D multiecho gradient echo sequence. Experimental studies demonstrated that phase fluctuations and image artifact levels in images and T2*mapping were significantly reduced after phase correction.2. Navigator echo can effectively track rigid-body motion of limited amplitude. However, lines associated with significant motion are uncorrectable and need to be discarded. Compressed sensing states that images with a sparse representation in a given domain can be accurately reconstructed from undersampled datasets by using a nonlinear reconstruction. In this study, a pseudo-random k-space trajectory was used and motion was detected by navigator echo. After discarding the motion corrupted lines in k-space, the randomly undersampled dataset can be accurately reconstructed with compressed sensing methods. Experimental studies demonstrated that motion artifacts were reduced dramatically after correction.