Axial variation of deoxyhemoglobin density as a source of the low-frequency time lag structure in blood oxygenation level-dependent signals
Fig 9
Analysis of the signal components and the lag structure.
(A) S0 and T2* signals were interpolated based on multi-echo acquisitions at short and typical TEs for BOLD fMRI. The lag map created from the S0 image shows a unique structure but fails to reflect the arterial and venous structures that are consistently found in the BOLD lag map. Using the T2*-weighted signals, the lag map changes upon respiratory challenges, which should primarily reflect the modification of the perfusion pattern; however, an interaction with the signal component is not excluded. The right panels show intraclass correlation coefficients as a quantitative measure of within-participant image similarity with the BOLD lag map, with error bars indicating 95% confidence intervals. (B) Temporal profiles from the 3 vascular regions indicate an absence of region effects in the S0 signal, suggesting a globally uniform mechanism underlying the S0 response. BOLD, blood oxygen level-dependent; ICC, interclass coefficient; TE, echo time; fMRI, functional magnetic resonance imaging; sLFO, spontaneous low-frequency oscillation.