@article {aja2011statistical, title = {Statistical noise analysis in GRAPPA using a parametrized noncentral Chi approximation model}, journal = {Magnetic resonance in medicine}, volume = {65}, number = {4}, year = {2011}, pages = {1195{\textendash}1206}, publisher = {Wiley Subscription Services, Inc., A Wiley Company}, author = {Santiago Aja-Fern{\'a}ndez and Antonio Trist{\'a}n-Vega and W Scott Hoge} }