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1. #ANALYSIS OF FUNCTIONAL MRI TIME SERIES. HUMAN BRAIN MAPPING SERIES#
2. #ANALYSIS OF FUNCTIONAL MRI TIME SERIES. HUMAN BRAIN MAPPING WINDOWS#

This results in a significant boost in temporal signal-to-noise ratio (TSNR) that permits the detection of interesting phenomena commonly buried below noise levels in single-echo fMRI.

#ANALYSIS OF FUNCTIONAL MRI TIME SERIES. HUMAN BRAIN MAPPING SERIES#

At the SFIM we are developing a series of algorithms that exploit this TE/non-TE dependence to automatically separate BOLD (such as neuronally induced signal changes) from non-BOLD fluctuations (e.g., subject motion, hardware instabilities, inflow effects, etc.). Fortunately, many of these nuisance fluctuations are non-TE dependent, while neuronally induced fluctuations are heavily dependent on the selected TE. In addition to neuronally induced fluctuations (the ones of interest for most experiments), the fMRI signal also contains nuisance signal fluctuations due to hardware instabilities, progressive heating, subject motion, respiration, cardiac function, inflow related signals, etc. Functional MRI time-series contain fluctuations of many different origins. The question then is: it is worth acquiring these additional data at suboptimal TEs? If so, why? At the SFIM, we believe it is extremely useful.

Such acquisition schemes are commonly referred to as multi-echo fMRI (ME-fMRI).

#ANALYSIS OF FUNCTIONAL MRI TIME SERIES. HUMAN BRAIN MAPPING WINDOWS#

In practice, nothing precludes researchers from having additional readout windows centered at TEs (delays from the RF pulse) other than the optimal TE discussed above. Because data is acquired at only one time-delay (the TE) from each RF pulse, it is common to refer to this data acquisition scheme as single-echo fMRI. For Blood Oxygen Level Dependent (BOLD) fMRI, which is interested in T2* signal fluctuations, it is desirable to setup the TE as close as possible to the T2* of grey matter (GM). This TE, which is setup by the experimenter, depends on factors such as field strength (e.g., 1.5T, 3T, 7T), target tissue (e.g., GM, WM, CSF), and target imaging parameter (e.g., T1, T2, T2*). The receiving elements at the scanner record signals during a readout window centered on the echo time (TE) which is the moment when the recoverable signal of interest is maximized. Most fMRI echo-planar imaging (EPI) techniques acquire a single brain volume of data per radio-frequency (RF) excitation pulse.