CONSTRUCTION OF A WHOLE-BODY BLOOD-FLOW MODEL FOR USE IN POSITRON-EMISSION-TOMOGRAPHY IMAGING WITH [O-15]WATER

A whole body bloodflow model (WBBFM) was developed and tested using ST ELLA II, an icon-driven mathematical simulation software package. The WBBFM uses parallel chambers to represent gray and white areas of the brain, body organs such as lungs, heart (right and left halves), injec tion site, and blood sampling sites. Input values to the WBBFM include organ blood flows, organ volumes, tissue:blood partition coefficients , injected activity, and data acquisition times for a positron emissio n tomography (PET) camera. Input variables included an injection funct ion (e.g., bolus), and a blood flow function (e.g., transient variatio ns inflow). The kinetic behavior of [O-15]water, a freely diffusible r adiotracer employed in PET to characterize blood flow was examined by the WBBFM. The physiologic behavior of water in the human body was emu lated using the WBBFM and the model's predictive value was verified by comparing calculated results with the following properties of water: diffusibility, tissue:blood partition coefficient of [O-15]water, and the mixing of[O-15]water with total body water. The WBBFM simulated Ke ty's autoradiographic method used in the estimation of regional cerebr al blood flow by PET using [O-15]water. The application of the model t o a cognitive activation study paradigm based on Kety's method is pres ented and its results compared to published literature data. With appr opriate modification in the half-life, tissue:blood partition coeffici ent, and the amount of administered radioactivity, the WBBFM should pr ove useful as a tool to examine kinetics of other freely diffusible ra diotracers used in PET.