Phase stability in fMRI time series: effect of noise regression, off-resonance correction and spatial filtering techniques.

Although the majority of fMRI studies exploit magnitude changes only, there is an increasing interest regarding the potential additive information conveyed by the phase signal. This integrated part of the complex number furnished by the MR scanners can also be used for exploring direct detection of neuronal activity and for thermography. Few studies have explicitly addressed the issue of the available signal stability in the context of phase time-series, and therefore we explored the spatial pattern of frequency specific phase fluctuations, and evaluated the effect of physiological noise components (heart beat and respiration) on the phase signal.

Advantages of using multiple-echo image combination and asymmetric triangular phase masking in magnetic resonance venography at 3 T.

The present work explores the possibility of localizing veins with magnetic resonance venography using susceptibility weighted imaging. It also seeks new approaches, directed by the spatial specificity of activated brain regions, that have sufficient precision for practical use in functional MRI studies. A 3D flow compensated multiple gradient echo sequence, featuring optimized T2* weighting within a reasonable time of acquisition (11 min) and a small voxel size (0.

The effect of physiological noise in phase functional magnetic resonance imaging: from blood oxygen level-dependent effects to direct detection of neuronal currents.

Recently, the possibility to use both magnitude and phase image sets for the statistical evaluation of fMRI has been proposed, with the prospective of increasing both statistical power and the spatial specificity. In the present work, several issues that affect the spatial and temporal stability in fMRI phase time series in the presence of physiologic noise processes are reviewed, discussed and illustrated by experiments performed at 3 T. The observed phase value is a fingerprint of the underlying voxel averaged magnetic field variations.

Voxel-based analysis of R2* maps in the healthy human brain.

Purpose: To develop a voxel-based analysis of an R2* map of healthy human brain that is automatic, reproducible, and realizable in a single examination on a 3T MR imager. Such a tool could be useful to measure iron accumulation in neurodegenerative diseases.

Materials And Methods: In all, 18 healthy subjects underwent MR imaging at a field strength of 3T: 1) six consecutive T2*-weighted gradient-echo volumes were acquired using a segmented echo-planar imaging sequence and 2) a conventional dual-echo turbo spin echo sequence was also applied to acquire T2-weighted images.