Hemodynamic Response Latency Analysis Using Wavelet Transform in Event-related Functional MRI

Many studies showed that the hemodynamic response (HR) to brief neural activity caused by the blood oxygen level-dependent effect is delayed some seconds, and that the HR latency (= time to peak from neural activation) varies among activation sites. This paper proposes a novel method for estimating HR latency by analyzing event-related functional magnetic resonance images based on a continuous wavelet transform. The proposed method can simultaneously detect activation areas and estimate the HR latency. We also studied variability of the HR latency across subjects within the same activation sites, across acquisition days within a subject, and among activation sites within a subject. The experiments were done on 10 healthy subjects with hand-gripping tasks. We found no significant difference of HR latencies at a given activation site within a subject across acquisition days. And, we found significant differences of HR latency between the supplementary motor area (SMA) and the primary motor cortex (M1) in individual subjects, and among subjects.