Validity of the Noncentral Chi Model in Multiple-Coil Systems with Noise Correlations

Santiago Aja-Fernandez¹, Antonio Tristan-Vega²

Noise in the composite magnitude signal (CMS) from multiple-coil systems is usually assumed to follow a noncentral chi distribution. However, this is true only if the variance of noise is the same for all coils, and no correlation exists between them. If the covariance matrix is not diagonal, the distribution of the CMS is not strictly a noncentral chi. It could be modeled as such only if the coefficient of correlation is small enough and effective values are considered. This will imply a reduced effective number of coils and an increased effective variance of noise.