RENAL KINETIC PARAMETERS ESTIMATION FROM FAST ACTIVITY CURVES SAMPLING WITH A THREE-HEADED SPECT SYSTEM

摘要

Recently, we proposed a technique that allows to achieve a subsecond sampling of the time-activity curves (TACs) in specific regions of interest (ROI) of the human body when data are acquired with a three-headed Single Photon Emission Computed Tomography (SPECT) system. This technique has been applied in renal studies for the determination of the blood pool input function and of the renal TACs (sampling interval: 0.67 sec). A new simple data analysis method has been developed for the estimation of the renal clearance values directly from the comparison of these curves, that were related by defining a kinetic model for the behavior of the tracer. The approach is in principle analogous to the conventional one of fitting the tracer kinetic model to the TACs generated from the ROIs segmented on a temporal series of images, but the new fast sampling procedure is not affected by the problems of inconsistency of data and unbiased estimates can be retrieved. The method has been compared with the Direct Least Squares Estimation (DLSE) method by means of simulations and it has shown many advantages both under the computational and the theoretical aspects. The number of equations is strongly reduced and iterative estimation can be avoided; the number of unknowns is reduced too, since the method does not require the description, often not realistic at all, of the tracer behavior in regions different from kidneys and blood.