A model for susceptibility artefacts from respiration in functional echo-planar magnetic resonance imaging

Respiration causes variations in the signals acquired during magnetic reson ance imaging (MRI) and therefore is a significant source of noise in Functi onal brain imaging. A primary component of respiratory noise may arise from variations of bulk susceptibility or air volume in the chest. Here we inve stigate the nature of the image artefacts that can be caused by such change s. We develop a simple model which attempts to mimic the effects of variati ons in susceptibility and volume during respiration. Theoretical calculatio ns, computer simulations and imaging experiments with this model show that small variations in susceptibility within the thorax from alterations in th e paramagnetism of cavity gas may lead to a shift of the image on the order of 0.1 pixels as well as a shading of the intensity by +/-1%. These effect s are observed to he predominant in the phase-encoding direction. They may lead to the production of spurious activations in functional MRI and are li kely to be of more importance at higher field strengths.