Conventional analysis of functional magnetic resonance imaging (fMRI) data using the general linear model (GLM) employs a neural model convolved with a canonical hemodynamic response function (HRF) peaking 5 s after stimulation. Incorporation of a further basis function, namely the canonical HRF temporal derivative, accounts for delays in the hemodynamic response to neural activity. A populatio...

Functional magnetic resonance imaging (fMRI) is an indirect measure of brain activity, i.e. it is a convolution of the latent (unmeasured) neural signal and the hemodynamic response function (HRF). As such, the HRF has been shown to vary across brain regions and individuals. The shape of the HRF is controlled by both neural and non-neural factors. The shape of the HRF can be characterized by th...

Abstract Although several functional magnetic resonance imaging (fMRI) studies have been conducted in human models of mild traumatic brain injury (mTBI), to date no studies have explicitly examined how injury may differentially affect both the positive phase of the hemodynamic response function (HRF) as well as the post-stimulus undershoot (PSU). Animal models suggest that the acute and semi-ac...

Functional magnetic resonance imaging (fMRI) is a noninvasive technique used to detect brain activity. It utilizes the fact that the magnetic resonance signal intensity is correlated with the cerebral blood flow, which in turn is correlated with neural activity [4]. Hence, fMRI can localize brain regions that show significant neural activity upon stimulus presentation, where the stimulus is des...

INTRODUCTION Over the past five years, functional magnetic resonance imaging (fMRI) of the human spinal cord has been developed and proven effective for localizing areas of neuronal activity within the spine in response to sensory stimuli [1]. However, fMRI of the spinal cord is currently not as reliable as fMRI of the brain because of several spine-specific issues. Breathing and heart-rate, as...

The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. Here, we used functional photoacoustic microscopy (fPAM) to investigate single cerebral blood vessels of rats after left forepaw stimulation. In this system, we analyzed the spatiotemporal evolution of the HRFs of the total hemog...

Optimal experimental design for estimation of the hemodynamic response function (HRF) is investigated using a nonlinear model with a quadratic mean squared error design criterion. This criterion is used, along with a genetic algorithm, to select locally optimal designs that are shown to be, in most cases, more efficient than designs selected with the more commonly used linear expansion criterio...

Many fMRI analysis methods use a model for the hemodynamic response function (HRF). Common models of the HRF, such as the Gaussian or Gamma functions, have parameters that are usually selected a priori by the data analyst. A new method is presented that characterizes the HRF over a wide range of parameters via three basis signals derived using principal component analysis (PCA). Covering the HR...

Introduction A limitation of T2weighted BOLD fMRI is the confounding contribution of signal from the larger vasculature. An improved BOLD specificity to parenchyma can be achieved at high field strengths such as 7T due to increased contrast-to-noise ratio, and reduced contribution of intravascular signal as compared to lower field strengths. Moreover, at 7T high spatial and temporal resolution ...