A fluid injector system for delivering a multi-phase fluid injection to a patient and methods of fluid delivery is disclosed. Methods of creating and using a multi-aspect fluid path impedance model of the injector system are used. Modeling and adjustment of factors that affect impedance and prevent or reduce backflow, reduce the likelihood of fluid flow rate spikes and provide more accurate flow rates and mixing ratios of fluids may be repeated or happen essentially continuously during an injection. The adjustments may be determined before the injection or determined and/or adjusted during the injection. The determination may include sensor feedback commonly used in injectors such as pressure and position feedback as well as other sensors. In all cases, the user can be notified of adjustments through on-screen notices and/or through the recordation of the injection data by a control device of the injector at the conclusion of the injection.
