Parametric imaging of patient pharmacokinetics

This paper presents an approach to extracting patient pharmacokinetic information from a set of longitudinal scintigraphic images and representing the kinetic information in parametric image form. In this approach, three or four pairs of simultaneously acquired anterior and posterior images, for internal dosimetry with iodine-131, are obtained at 24-h intervals. Each pair of anterior and posterior images is converted to a "conjugate-view" image. The sequential conjugate-view images are then spatially registered to each other using a symmetric phase-only matched filter technique. With the registered images, the value at each pixel location, over time, is fitted to a monoexponential function. The resulting decay constant and intercept parameters are then represented as "decay-constant" and "intercept" images. Further analytical integration of the exponential function results in a "cumulated-activity" image. Phantom studies demonstrated that the proposed method is accurate and reliable in the registration and kinetic data extraction of the longitudinal images. Clinical application of the approach to patients with thyroid carcinoma showed that regions of rapid uptake or clearance that would not otherwise be highlighted were easily identified and some regions with unexpected kinetics were observed. It is concluded that decay-constant, intercept, and cumulated-activity images provide a rapid and comprehensive visual assessment of patient pharmacokinetics. The technique may have a greater impact on the care of patients with extensive and distributed disease.