Abstract: The present invention recited a method and apparatus for measuring a parameter of a fluid within a fluid channel using a tracer element injection by an injection element and detected by a detection element at a location separate from the injection element location. The injection element and detection element of the present invention are in communication with a computational element, wherein the computation element is capable of measuring a parameter of a fluid in a fluid channel based upon time of flight data derived from the injection element and the detection element.