Figure 6
The effect of motion on the spatial response (PSF) of a point source using a 2D chemical shift imaging (CSI) sequence (matrix: 32 \(\times\) 16, FoV: 320 \(\times\) 160 mm, TR: 2 s, 1 average). The spherical phantom (\(d = {20}\) mm) was filled with a concentrated phosphorus solution, moving periodically about the center position. Motion was step-wise by 4 mm per TR along the head-foot (HF) direction with maximal displacement of \(\Delta z = {40}\) mm. The first row displays the PSF derived from a simulation of the described phantom, motion and scan parameters. Plots in the second row show the real part of the actually measured and voxel-wise fitted spectral signal, spatially interpolated (5 \(\times\)) for better visualization. The compensated scan (MoCo) recovers the PSF of the static scan to a high degree. The non-compensated scan (NoCo) suffers substantial motional blurring and ghosting, visible from the signal loss in the center, a broadened PSF, articulate side lobes and signal bleed further from the center. Simulation and measurement are coherent. The remaining motion artifacts in the experimental data are also apparent in the simulation by incorporating the appropriate latency to the motion update (indicated by the white arrows).
