TY - JOUR
T1 - The phase shift index for marking functional asynchrony in Alzheimer's disease patients using fMRI
AU - Xu, Yin
AU - Xu, Guofan
AU - Wu, Gaohong
AU - Antuono, Piero
AU - Rowe, Daniel B.
AU - Li, Shi Jiang
N1 - Funding Information:
This study was supported, in part, by the Extendicare Foundation, the Dana Foundation and research grants AG20279 and RR00058 from the National Institutes of Health. The authors thank C.M. O'Connor, MA, for editorial assistance.
PY - 2008/4
Y1 - 2008/4
N2 - Our previous study suggested that the functional magnetic resonance imaging MRI (fMRI) COSLOF Index (CI) could be used as a quantitative biomarker for Alzheimer's disease (AD). The fMRI CI was lowest in the AD group (0.13±0.10), followed by the mild cognitive impairment (MCI) group (0.20±0.05) and the control group (0.34±0.09). The current study continues an investigation into which of the following two factors has a dominant role in determining the CI: the signal-to-noise ratio (SNR) or the phase shift of spontaneous low-frequency (SLF) components. By using a theoretical model for SLF components, we demonstrated that the normalized CI does not depend on the SNR of the SLF components. Further analysis shows that by taking the ratio of the cross-correlation coefficient to the maximum-shifted cross-correlation coefficient, the SNR factor can be canceled. Therefore, the determination of the phase shift index (PSI) method is independent of the SNR, and the PSI provides an accurate measure of the phase shift between SLF components. By applying this PSI method to the control, MCI and AD groups of subjects, experimental results demonstrated that the PSI was highest in the AD group (72.6±11.3°), followed by the MCI group (58.6±5.7°) and, finally, the control group (40.6±8.4°). These results suggest that the larger is the PSI value, the more asynchrony exists between SLF components.
AB - Our previous study suggested that the functional magnetic resonance imaging MRI (fMRI) COSLOF Index (CI) could be used as a quantitative biomarker for Alzheimer's disease (AD). The fMRI CI was lowest in the AD group (0.13±0.10), followed by the mild cognitive impairment (MCI) group (0.20±0.05) and the control group (0.34±0.09). The current study continues an investigation into which of the following two factors has a dominant role in determining the CI: the signal-to-noise ratio (SNR) or the phase shift of spontaneous low-frequency (SLF) components. By using a theoretical model for SLF components, we demonstrated that the normalized CI does not depend on the SNR of the SLF components. Further analysis shows that by taking the ratio of the cross-correlation coefficient to the maximum-shifted cross-correlation coefficient, the SNR factor can be canceled. Therefore, the determination of the phase shift index (PSI) method is independent of the SNR, and the PSI provides an accurate measure of the phase shift between SLF components. By applying this PSI method to the control, MCI and AD groups of subjects, experimental results demonstrated that the PSI was highest in the AD group (72.6±11.3°), followed by the MCI group (58.6±5.7°) and, finally, the control group (40.6±8.4°). These results suggest that the larger is the PSI value, the more asynchrony exists between SLF components.
KW - Alzheimer's disease
KW - Phase shift index
KW - fMRI
KW - functional synchrony
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U2 - 10.1016/j.mri.2007.07.007
DO - 10.1016/j.mri.2007.07.007
M3 - Article
C2 - 18164158
AN - SCOPUS:40049107147
SN - 0730-725X
VL - 26
SP - 379
EP - 392
JO - Magnetic Resonance Imaging
JF - Magnetic Resonance Imaging
IS - 3
ER -