On the water–fat in-phase assumption for quantitative susceptibility mapping
Christof Boehm, Sarah Schlaeger, Jakob Meineke, Kilian Weiss, Marcus R. Makowski, Dimitrios C. Karampinos
Purpose
To (a) define multi-peak fat model-based effective in-phase echo times for quantitative susceptibility mapping (QSM) in water–fat regions, (b) analyze the relationship between fat fraction, field map quantification bias and susceptibility bias, and © evaluate the susceptibility mapping performance of the proposed effective in-phase echoes in comparison to single-peak in-phase echoes and water–fat separation for regions where both water and fat are present.
Methods
Effective multipeak in-phase echo times for a bone marrow and a liver fat spectral model were derived from a single voxel simulation. A Monte Carlo simulation was performed to assess the field map estimation error as a function of fat fraction for the different in-phase echoes. Additionally, a phantom scan and in vivo scans in the liver, spine, and breast were performed and evaluated with respect to quantification accuracy.
Results
The use of single-peak in-phase echoes can introduce a worst-case susceptibility bias of 0.43 ppm. The use of effective multipeak in-phase echoes shows a similar quantitative performance in the numerical simulation, the phantom and in all in vivo anatomies when compared to water–fat separation-based QSM.
Conclusion
QSM based on the proposed effective multipeak in-phase echoes can alleviate the quantification bias present in QSM based on single-peak in-phase echoes. When compared to water–fat separation-based QSM the proposed effective in-phase echo times achieve a similar quantitative performance while drastically reducing the computational expense for field map estimation.