Artificial shifting of fMRI activation localized by volume- and surface-based analyses.
Spatial smoothing is an important post-processing procedure that is used to increase the signal-to-noise ratio (SNR) of blood oxygenation level-dependent signals (BOLD) in common functional magnetic resonance imaging (fMRI) applications. However, recent studies have shown that smoothing artificially shifts probabilistic local maxima of fMRI activations. In this study, we show shifting of the localization of functional centers in hand motor areas of the cerebral cortex by three-dimensional isotropic Gaussian kernel smoothing or two-dimensional heat kernel smoothing in volume- and surface-based fMRI analyses. Activation maps derived from smoothed echo planar imaging (EPI) data by volume- and surface-based analyses were assigned to the nodes of individual cortical surface models, and local maxima in the primary motor area (M1) and the primary somatosensory cortex (S1) were compared with those derived from non-smoothed risk map analysis, which is commonly used in presurgical applications. For each analysis, the Euclidean and geodesic distances between the correlation coefficients of local maxima derived from smoothed and non-smoothed EPI data were measured. The results show that the correlation coefficients derived from the volume- and surface-based analyses were about 29.4% and 42.9% higher for smoothed than for non-smoothed risk map analyses, and show minimum shifting of localizations by 12.1 mm and 6.9 mm on average in Euclidean distance, respectively, and about 9.5 mm and 5.7 mm on average in geodesic distance, respectively.
Jo
Hang Joon
HJ
Department of Biomedical Engineering, Hanyang University, Sungdong P.O. Box 55, Seoul 133-605, South Korea.
Lee
Jong-Min
JM
Kim
Jae-Hun
JH
Choi
Chi-Hoon
CH
Gu
Bon-Mi
BM
Kang
Do-Hyung
DH
Ku
Jeonghun
J
Kwon
Jun Soo
JS
Kim
Sun I
SI
D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000706:statistics & numerical data*; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D009044:Motor Cortex / Q000033:anatomy & histology / Q000502:physiology; D016011:Normal Distribution; D010100:Oxygen / Q000097:blood; D013003:Somatosensory Cortex / Q000033:anatomy & histology / Q000502:physiology
D010100:Oxygen