Ronja Berg^{1}, Jakob Meineke^{2}, Andreas Hock^{3}, Claus Zimmer^{1}, and Christine Preibisch^{1}

Quantitative Susceptibility Mapping (QSM) has recently been used for assessing the cerebral oxygen metabolism. However, a systematic investigation on the most suitable imaging parameters and reconstruction algorithms for determining the venous susceptibility values is missing. Therefore, we investigated both, the impact of flow compensation and accelerated acquisition as well as different reconstruction methods on measured venous susceptibility. Our results suggest that the choice of reconstruction technique can significantly influence the venous susceptibility values while the investigated imaging parameters did not considerably affect its accuracy. Thus, the applied QSM reconstruction technique has to be considered carefully when quantifying the venous oxygenation.

A
standard SWI sequence with first-echo only FC and with CS
acceleration factor 3 can be used for analysis of venous oxygenation
via QSM reconstruction. Proper
validation of
susceptibility values obtained with different QSM algorithms requires
further studies and
comparisons with alternate methods, e.g. TRUST.^{2,18}

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**Figure 1: QSM parameter maps from three SWI sequences and six QSM reconstruction methods.**

Top row: SWI with first-echo flow compensation only. Middle row: SWI with full multi-echo flow compensation; both sequences using SENSE (SENSE-factor 2). Bottom row: SWI with full multi-echo flow compensation using Compressed Sense (CS=3). Columns: QSM maps obtained using FANSI reconstruction, MEDI toolbox, and STI Suite with two different parameter settings each. Processing parameters are provided below the corresponding QSM images. FC = flow compensation, ME = multi-echo, LBV = Laplacian-boundary-value, BET = brain-extraction-tool, FIT = fractional-intensity-threshold, TG = threshold-gradient, PDF = projection-onto-dipole-fileds; SMV = spherical-mean-value.

**Figure
2: Comparison of automatic vessel segmentations of two SWI sequences
and three QSM reconstruction methods.**

Results from the multiscale
vessel filtering (blue overlay) from the JIST-LayoutToolbox for SWI
with first-echo flow compensation only (top row) and with full
multi-echo flow compensation (bottom row). Results for one parameter
setting of each reconstruction algorithm (FANSI, MEDI, and STI Suite)
are shown in each column. Processing parameters are provided below
the corresponding QSM images. A Hessian shape filter was used for the
segmentation. The parameters were: probability threshold = 0.3,
propagation model: diffusion with diffusion factor = 0.5.

**
Figure
3: Mean susceptibility values obtained from automatically segmented
QSM voxels for all sequences and reconstruction methods.**

Box plots of the mean
susceptibility values of the segmented voxels for all 7 subjects
comparing values for two different parameter settings from three
reconstruction algorithms (FANSI, MEDI, and STI Suite). Results are
shown for SWI sequences with first-echo flow compensation (green),
with full multi-echo flow compensation (orange), and with multi-echo
flow compensation with Compressed Sense (blue). For the automatic
segmentation, the multiscale vessel filtering method from the
JIST-LayoutToolbox was used.

**
Figure
4: Exemplary manual segmentation of a vessel, for different
reconstruction methods. **

a) Summation of automatically
segmented voxels from all six reconstructions (two from FANSI, MEDI,
and STI, respectively). Color coding depends on the number of
reconstructions for which a specific voxel was segmented. b) SWI of
an enlarged exemplary vessel with blue overlay of the manual
segmentation for first-echo only FC (top) and multi-echo FC (bottom).
c) The same section of the enlarged vessel is shown for FANSI 2, MEDI
2, and STI STAR reconstruction methods in both sequences. The green
arrows indicate inhomogeneous structures.

**Figure 5: Mean susceptibility values of manually segmented QSM vessels.**

Box plots of mean susceptibility values of four manually segmented ROIs for each of the seven subjects comparing values from two different parameters settings for each of the reconstruction algorithms (FANSI, MEDI, and STI Suite). For segmentation, ROIs in four larger vessels were selected in each subject. Each box plot visualizes the mean values of four ROIs in seven subject (28 values). Results are shown for SWI sequences with first-echo flow compensation (green), with full multi-echo flow compensation (orange), and with multi-echo flow compensation with Compressed Sense (blue). **
**