Functional MRI is based on changes in cerebral microvasculature triggered by increased neuronal oxidative metabolism. This change in blood flow follows a pattern known as the hemodynamic response function (HRF), which typically peaks 4-6 s following stimulus delivery. However, in the presence of cerebrovascular disease the HRF may not follow this normal pattern, due to either the temporal signa...

Introduction Brain areas are additionally activated in elderly subjects [1,2]. It was suggested that this additional recruitment of brain areas in elderly subjects was consistent with the compensation hypothesis and characterized neuroplasticity at the systems level in the aging brain, rather than dedifferentiation hypothesis [2]. On the other hand, age-related reduction of BOLD signal (hemodyn...

Signal detection in noisy data set is a common problem in signal processing. Detection of the hemodynamic response function (HRF) embedded in randomized event-related fMRI (rER-fMRI) time series is an example of this problem. So far, most studies that set out to obtain unbiased HRF use some forms of time-window (TW) averaging method to extract HRF from the rER-fMRI data. In this paper we applie...

Functional magnetic resonance imaging (fMRI) signal variations are based on a combination of changes in cerebral blood flow (CBF) and volume (CBV), and blood oxygenation. We investigated the relationship between these hemodynamic parameters in the rodent barrel cortex by performing fMRI concurrently with laser Doppler flowmetry (LDF) or optical imaging spectroscopy (OIS), following whisker stim...

INTRODUCTION A fixed hemodynamic response function (HRF) is commonly used for functional magnetic resonance imaging (fMRI) analysis. However, HRF may vary from region to region and subject to subject. We investigated the effect of locally estimated HRF (in functionally homogenous parcels) on activation detection sensitivity in a heroin cue reactivity study. METHODS We proposed a novel explora...