Fundamentals of tracer kinetics for radiologists

With the increasing application of dynamic and functional techniques to radiological imaging modalities other than nuclear medicine, it is becoming increasingly important for radiologists to understand the principles of tracer kinetics and for functional and physiological aspects of imaging to be expanded in radiological training. Tracer, or indicator, kinetics can be broken down in six fundamental physiological variables (transit time, distribution volume, clearance, extraction fraction, blood flow and permeability-surface area product), three fundamental physical variables (time, mass and volume) and three fundamental equations (transit time equation, dilution equation and Fick equation). This teaching review defines the six fundamental physiological variables, discusses their relevance to functional imaging and describes how they may be measured using radiological techniques. It also illustrates how most of their tracer kinetics are based on one or other of the three fundamental equations.