Improving quantitative susceptibility mapping using iterative restoration of the fringe phase (REFRASE)
13th May 2021
Johannes Lindemeyer, Wieland A. Worthoff, Aliaksandra Shymanskaya and N. Jon Shah
Quantitative susceptibility mapping (QSM) is a relatively new MRI technique used to measure the spatial distribution of magnetic susceptibility within biological tissues, quantitatively. However, reconstructed results can be critically biased by misinterpreted or missing phase data near the edges of the brain support. These data either have to be excluded, which can result in the loss of potentially important details, or corrected before further processing can take place. This research aims to address this problem using a novel iterative approach entitled REFRASE - restoration of the fringe phase.
REFRASE works by simultaneously enhancing the accuracy of multi-echo phase data QSM maps and the extent of the area available for evaluation. Data loss caused by strong local phase gradients near the surface of the brain support is recovered within the original phase data using harmonic and dipole-based fields extrapolated from a robust support region. Over several iterations, phase data are rectified prior to the application of further QSM processing steps.
The concept was successfully validated on numerical phantoms and brain scans from a cohort of volunteers. The results showed the increased extent of the mask and improved numerical stability within the segmented globus pallidus, confirming the efficacy of the presented method in comparison to traditional evaluation.
The presented method is expected to be very valuable for low-resolution field mapping approaches that suffer from strong intra-voxel gradients, and the free choice of the background estimation method renders REFRASE a universal tool for arbitrary phase contrast applications. It is further anticipated that as ultrahigh field MRI becomes more accessible, the method will evolve to its full potential, compensating for stronger local magnetic field gradients.
Original publication