Prog Med Phys.  2013 Mar;24(1):25-34.

Voxel-based Investigations of Phase Mask Effects on Susceptibility Weighted Images

• Hwang EJ
• Kim MJ
• Kim HG
• Ryu CW
• Jahng GH

Abstract

To investigate effects of phase mask on susceptibility-weighted images (SWI) using voxel-based analyses in normal elderly subjects. A three-dimensional (3D) gradient echo sequence ran to obtain SWIs in 20 healthy elderly subjects. SWIs with two (SWI2) and four (SWI4) phase multiplications were achieved with positive (PSWI) and negative (NSWI) phase masks to investigate phase mask effects. The voxel-based comparisons were performed using paired t-tests between PSWI and NSWI and between SWI2 and SWI4. Differences of signal intensities between magnitude images and SWI4 were larger than those between magnitude images and SWI2s. Differences of signal intensities between magnitude images and PSWIs were larger than those between magnitude images and NSWIs. Moreover, the signal intensities from NSWI2s and NSWI4s were greater than those from PSWI2s and PSWI4s, respectively. More differences of signal intensities between NSWI4 and PSWI4s were found than those between NSWI2s and PSWI2s in the whole brain images. The voxel-based analyses of SWI could be beneficial to investigate susceptibility differences on the entire brain areas. The phase masking method could be chosen to enhance brain tissue contrast rather than to enhance venous blood vessels. Therefore, it is recommended to apply voxel-based analyses of SWI to investigate clinical applications.

Keyword

Susceptibility Weighted Imaging (SWI); Phase mask; Voxel-wise investigation

MeSH Terms

Aged
Blood Vessels
Brain
Humans
Masks

Figure

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  Fig. 1. The representative whole brain images obtained from a healthy human subject. Magnitude (a), phase (b), positively phase-masked susceptibility-weighted image (SWI) with 2 phase mask multiplications (PSWI2, c), negatively phase-masked SWI with 2 phase mask multiplications (NSWI2, d), positively phase-masked SWI with 4 phase mask multiplications (PSWI4, e), negatively phase-masked SWI with 4 phase mask multiplications (NSWI4, f).

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  Fig. 2. Results of voxel-wise comparisons between magnitude images and positively (P) phase-masked susceptibility weighted images (SWIs) with two different phase mask multiplications. Comparison between magnitude images and positively phase-masked SWI with 2 phase mask multiplications (magnitude＞ PSWI2, a) and between magnitude images and positively phase-masked SWI with 4 phase mask multiplications (magnitude＞PSWI4, b). No significant differences were found between P_SWI2 and P_SWI4.

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  Fig. 3. Results of voxel-wise comparisons between magnitude images and negatively (N) phase- masked susceptibility weighted image (SWI) with two different phase mask multiplications. Comparisons between magnitude images and negatively phase-masked SWI with 2 phase mask multiplications (magnitude＞NSWI2, (a), between magnitude images and negatively phase-masked SWI with 4 phase mask multiplications (magnitude＞NSWI4, (b), and between NSWI2 and NSWI4 (NSWI2＞NSWI4, c).

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  Fig. 4. Results of voxel-wise comparisons between susceptibility-weighted imaging (SWI) with the positive (P) phase mask and that with the negative (N) phase mask with the whole brain with the threshold of family-wise error rate (FWE) p=0.005. (a) Comparison between the whole brain negatively phase-masked SWI with 2 phase mask multiplications and positively phase-masked SWI with 2 phase mask multiplications (NSWI2＞ PSWI2). (b) Comparison between the whole brain negatively phase-masked SWI with 4 phase mask multiplications and positively phase-masked SWI with 4 phase mask multiplications (NSWI4＞PSWI4).

Reference

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