Tracer flows and 'difficult' organs

This paper describes a method for measuring tracer kinetics in organs which are larger than the field of view of a gamma camera, by performing initial dynamic studies on part of that organ, followed by a later study to determine the tracer content of the entire organ. Information is transferred from the measured data to 'absolute values' by means of a calculated intermediate number which is called the 'MTBE' (mean time in blood, equivalent). Initial testing of the technique with methylene diphosphonate (MDP) bone studies produced tracer flow rates of 0.000366 s-1 into bone and 0.001525 s-1 into interstitial fluid in patients with no known bone disease. Patients with active Paget's disease of bone had higher bone inflow rates, and showed some improvement following therapy with either editronate or pamidronate. The method has the potential to be applied to other situations, particularly SPET, using SPET to calculate tracer content and converting the results to flow rates using the formula: Inflow rate = Content/MTBE.