The Importance of Constraints in Factor Analysis of Dynamic Studies

A dynamic radionuclide study provides a description of the way the administrated tracer behaves in the several separate structures in the body. The usual aim of dynamic study analysis is to attempt to isolate the information from one or more important structures from the rest of the study. Because of the way the images of structures overlap it is rarely possible to derive the variation of tracer concentration within a single structure directly from the dynamic study. The common approach to this problem is to define a region (a region-of-interest (ROI)) around the structure of interest and compute the curve representing the variation of activity within that region and then attempt to estimate and remove from this curve the contribution from the surrounding and overlapping structures (background structures). An estimate of this component of activity is usually obtained from a second ROI over a region in the study indicative of the background activity in the region of the structure of interest.