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...

introduction: prior studies comparing hemodynamic response function (hrf) in the young and elderly adults based on fmri data have reported inconsistent findings for brain vision and motor regions in healthy aging. it is shown that the averaging method employed in all previous works has caused this inconsistency. the averaging is so sensitive to outliers and noise. however, fmri data are obscure...

Introduction: Prior studies comparing Hemodynamic Response Function (HRF) in the young and elderly adults based on fMRI data have reported inconsistent findings for brain vision and motor regions in healthy aging. It is shown that the averaging method employed in all previous works has caused this inconsistency. The averaging is so sensitive to outliers and noise. However, fMRI data are o...

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...

fMRI is increasingly used to monitor the modulating effects of pharmacological agents on human brain function [1]. Often a generalized linear model approach [2] (e.g. SPM, http://www.fil.ion.ucl.ac.uk/spm/) is applied to analyze fMRI data. Within this toolbox, a canonical form of the hemodynamic response function (HRF) is used as a standard regressor to analyze the signal course of the measured...

Modern cognitive experiments in functional Magnetic Resonance Imaging (fMRI) often aim at understanding the temporal dynamics of the brain response in regions activated by a given stimulus. The study of the variability of the hemodynamic response function (HRF) and its characteristics can provide some answers. In this context, we aim at improving the accuracy of the HRF estimation. To do so, we...

In fMRI data analysis it has been shown that for a wide range of situations the hemodynamic response function (HRF) can be reasonably characterized as the impulse response function of a linear and time invariant system. An accurate and robust extraction of the HRF is essential to infer quantitative information about the relative timing of the neuronal events in different brain regions. When no ...

The hemodynamic response function (HRF) describes the local response of brain vasculature to functional activation. Accurate HRF modeling enables the investigation of cerebral blood flow regulation and improves our ability to interpret fMRI results. Block designs have been used extensively as fMRI paradigms because detection power is maximized; however, block designs are not optimal for HRF par...