RT Journal Article SR Electronic T1 A physiological model for representation of tracer activity in re-circulating venous and arterial blood JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 2047 OP 2047 VO 52 IS supplement 1 A1 Finbarr O'Sullivan A1 Jian Huang A1 Niall Fitzgerald A1 Mark Muzi A1 Kenneth Krohn YR 2011 UL http://jnm.snmjournals.org/content/52/supplement_1/2047.abstract AB 2047 Objectives The kinetic analysis of dynamic PET time-course data is dependent on knowledge of the arterial blood time-course as an input function (AIF). Increasingly, high-resolution sampling of arterial blood is not available so more limited data is used for determination of the AIF. We propose a parametric whole body circulation model allowing information from either arterial or venous samples (direct blood measurements or image derived) to be used to reconstruct the AIF. Methods The model uses a Markov chain formulation to track the progress of tracer atoms through vascular and extra-vascular physiological spaces of the body, including the left and right ventricle (LV/RV) chambers of the heart. Model parameters describe transition probabilities from one space to another. Model time-steps are individual beats of the heart. The numerical implementation allows predictions for tracer concentration in the relevant spaces to be generated simply and efficiently. Results Provided there is negligible extra-vascular extraction or excretion of tracer over the time-course of the study, there will be equilibration between the activity in the venous and arterial blood. This is a basic but important check. Since the LV and RV describe arterial and venous blood pools, the model predicted time-course in these spaces can be compared to measurements of activity in arterial and/or venous blood and optimized model parameters determined by least squares. With this approach the time-course of total activity in venous and arterial blood data are well described by the model. The approach was validated for a number of tracers, including water, verapamil, FDG and FLT. Conclusions We have developed a physiologic model for representation of tracer activity in circulating blood. It allows the AIF to be determined from venous and/or arterial data. Application to PET image data will enhance the ability to recover the AIFs from blood regions that comprise of both arterial and venous elements. Research Support NCI P01-CA-42045 and SFI MI-2007/00