A fluid injector system includes at least one injector for pressurizing and delivering at least one fluid from at least one fluid reservoir, at least one fluid path section providing fluid communication between a bulk fluid reservoir and a syringe connected to the at least one injector, and at least one sensor arranged along the at least one fluid path section. The at least one sensor includes an emitter configured to emit light through the at least one fluid path section, and a detector configured to receive the light emitted through the at least one fluid path section and generate an electrical signal based on at least one property of the received light. The fluid injector system may further include at least one processor programmed or configured to determine, based on the electrical signal generated by the detector, at least one of an identity of the at least one fluid present in the fluid path section, a concentration of the at least one fluid in the fluid path section, and at least one property of the fluid path section.