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Magnitude and phase signal detection in complexvalued fMRI data
 Magnetic Resonance in Medicine
"... In a recent paper on complexvalued functional magnetic resonance imaging (fMRI) detection by Lee et al. (2007), a statistical model for magnitude and phase changes is presented (1). This follows a line of published research on the topic (2–5) motivated by the fact that fMRI phase data contains bio ..."
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In a recent paper on complexvalued functional magnetic resonance imaging (fMRI) detection by Lee et al. (2007), a statistical model for magnitude and phase changes is presented (1). This follows a line of published research on the topic (2–5) motivated by the fact that fMRI phase data contains biological information regarding the vasculature contained within voxels (6,7). The Lee et al. (2007) model is elegant and computationally efficient, but there are four items regarding it that need to be clarified in addition to its relationship to the Rowe (2005) model (5). The Rowe (2005) model for detecting magnitude and phase changes in complexvalued data is yRtyIt xtcosutxtsinut RtIt [1] where at time t, t 1,...,n, yRt and yIt are the observed real and imaginary observations. In addition, xt is the magnitude signal, xt is the tth row of a design matrix X describing temporal magnitude changes, is a vector of magnitude regression coefficients, ut is the phase signal, ut is the tth row of a design matrix U describing temporal phase changes, is a vector of phase regression coefficients. Finally, Rt and It are the real and imaginary measurement error that are independent and identically distributed N(0,2) variables. Several hypothesis pairs are presented with suitable selection from C 0, C 0, D 0, and
Imaging Periodic Currents Using Alternating Balanced SteadyState Free Precession
"... Existing functional brain MR imaging methods detect neuronal activity only indirectly via a surrogate signal such as deoxyhemoglobin concentration in the vascular bed of cerebral parenchyma. It has been recently proposed that neuronal currents may be measurable directly using MRI (ncMRI). However, ..."
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Existing functional brain MR imaging methods detect neuronal activity only indirectly via a surrogate signal such as deoxyhemoglobin concentration in the vascular bed of cerebral parenchyma. It has been recently proposed that neuronal currents may be measurable directly using MRI (ncMRI). However, limited success has been reported in neuronal current detection studies that used standard gradient or spin echo pulse sequences. The balanced steadystate free precession (bSSFP) pulse sequence is unique in that it can afford the highest known SNR efficiency and is exquisitely sensitive to perturbations in free precession phase. It is reported herein that when a spin phaseperturbing periodic current is locked to an RF pulse train, phase perturbations are accumulated across multiple RF excitations and the spin magnetization reaches an alternating balanced steady state (ABSS) that effectively amplifies the