Biophysically motivated efficient estimation of the spatially isotropic [Formula: see text] component from a single gradient‐recalled echo measurement

PURPOSE: To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientation‐dependent part of [Formula: see text] using a single gradient‐recalled echo (GRE) measurement. METHODS: The proposed method utilized a temporal second‐order approximation of the hollow‐cylinder‐fiber model, in which the parameter describing the linear signal decay corresponded to the orientation‐independent part of [Formula: see text]. The estimated parameters were compared to the classical, mono‐exponential decay model for [Formula: see text] in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of [Formula: see text] , it was compared to the established phenomenological method for separating [Formula: see text] into orientation‐dependent and ‐independent parts. RESULTS: Using the phenomenological method on the classical signal model, the well‐known separation of [Formula: see text] into orientation‐dependent and ‐independent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed. CONCLUSIONS: Since the proposed second‐order model features orientation‐dependent and ‐independent components at distinct temporal orders, it can be used to remove the orientation dependence of [Formula: see text] using only a single GRE measurement.