Fig 1.
The steps used in the QSM process.
(A) Phase image, (B) unwrapped phase image, (C) internal field map, and (D) QSM in rat brain region. (E-G) The steps used in the extraction of prior information from magnitude images.
Fig 2.
Selection of the radius of the sophisticated harmonic artifact reduction for phase data (SHARP) filtering.
(A) Local fields and (B) QSMs (L1 regularization with λ = 10−3) calculated by varying the radius of SHARP filtering from 1 to 9 in 2-voxel steps. (C) Difference in line profile of reconstructed QSM among various radii. In this figure, path-based phase unwrapping is used. (D) The enlargement of the rectangular (dotted line) in (C).
Fig 3.
Flowcharts of processing steps of susceptibility-weighted images (SWI).
SWI combines both magnitude and a filtered phase map with a multiplicative relationship to enhance image contrast.
Fig 4.
Comparison of quantitative susceptibility map (QSM) based on path-based and Laplacian-based phase unwrapping.
Images computed using 3D path-based and Laplacian-based phase unwrapping are presented in the first and second columns from the left. The third column depicts the difference in the images in the first two columns. (A-C) Comparison of the unwrapped phase images with path-based and Laplacian-based algorithms. (D-F) Comparison of the local field (SHARP filtering with radius of 3 voxels). (G-I) Comparison of reconstructed QSM (L1 regularization with λ = 10−3). The arrows point to regions where significant differences between the images in the left and middle columns were observed. (K) Comparison of the measured susceptibility values in vessels from (J) the region-of-interest (ROI) (***p < 0.001).
Fig 5.
Influence of the Selection of the Lagrange parameter λ.
Plot of the measured susceptibility value from region-of-interest (E) across various λ by (A) L1 regularization and (B) L1 regularization with magnitude prior. At optimal weighting of λ = 10−1.6, L1 regularization resulted in 0.147 ppm. In contrast, at optimal weighting of λ = 10−1.2, L1 regularization with magnitude prior resulted in 0.155 ppm.
Fig 6.
Quantitative visualization of QSM of a normal rat brain in three orthogonal views.
Veins in the cortical and internal brain are indicated. (A) A 2.5-mm-thick maximum intensity projection (MIP) in coronal view, (B) axial view, and (C) sagittal view. The major veins are labeled, including the great cerebral vein (GCV) of Galen, intracortical penetrating venule, inferior sagittal sinus (ISS), longitudinal hippocampal vein (LHIV), medial collicular vein (MCOLV), superior olfactory sinus (SOS), superior sagittal sinus (SSS), straight sinus (STS), thalamostriate vein (THSV), transverse sinus (TRS), middle internal frontal vein (MIF), anterior striate vein (ASTR), posterior striate vein (PSTR), medial striate vein (MSTR), and rostral rhinal vein (RRHV).
Table 1.
Estimated SvO2 of seven regions of interest from seven Control group rats (%).
Fig 7.
Comparison of QSM and susceptibility-weighted imaging (SWI).
(A) A 2.5-mm-thick MIP of QSM in axial view. The cortex in dorsal and lateral brain are marked by the rectangles and magnified in (C). (B) A 2.5-mm-thick minimum intensity projection (mIP) of SWI with identical ROIs. (D) In the mIP of SWI, the vein has blooming artifacts and is difficult to identify. The arrows point to the significant difference between QSM and SWI.
Fig 8.
Illustration of differences in the intracortical penetrating vessels between SWI and QSM.
(A) A coronal slice from SWI. (B) A coronal slice from QSM. (C) Magnified view of a 3.5 × 3.5-mm2 region of SWI marked by red rectangle in A. The bright signal represents the through-plane cortical vessels. (D) Fewer and smaller bright signals in QSM. (E) Quantification of vessel size using the two methods. (*p < 0.05).
Fig 9.
Detection of the rehabilitation of intracortical venules in the rat brain after stroke.
(A) Triphenyl tetrazolium chloride (TTC)-stained slice for infarcted cortical area confirmation over time. (B) Representative of 2.5-mm-thick minimum intensity projection (mIP) of SWI over time. (C) Representative of 2.5-mm-thick average intensity projection (AIP) of QSM over time. (D) Representative of 2.5-mm-thick SvO2 map over time. The second figure in the first row illustrates the ROI selections on the contralateral (left) and ipsilateral (right) cortices. The arrows indicate angiogenesis at 7 and 10 days post-reperfusion. (E) (F) Comparison of SvO2 estimates and SpO2 measures on a post-stroke rat. (E) SvO2 estimates by QSM-mMRV and (F) SpO2 measures using the pulse oximeter on contralateral and ipsilateral cortices. (Mean and SD cross subjects are presented; *p < 0.05; **p < 0.01; ***p < 0.001).
Fig 10.
Influence of the selection of the prior information W.
(A) Illustrations of the binary weighting in three dimensions across different thresholds from 0 to 0.15 (Wx: weighting factor in x dimension; Wy: weighting factor in y dimension; Wz: weighting factor in z dimension;). (C) The reconstructed QSMs across different thresholds. (D) The susceptibility values measured from the region-of-interest (B) are the same as in Fig 4(J).