Scattered photons blur positron emission tomography images, degrading image resolution, contrast, and quantitative accuracy. No general correction for scattered photons has been found, because the spatial distribution of scattered photons has yet to be characterized. The investigators study photon scattering based on a state-of-the-art Monte Carlo computer program, developed at Los Alamos National Laboratory, that can provide more information than is readily measurable experimentally. At present, this powerful analysis technique requires enormous computational resources. The investigators evaluate the advantages of using a massively parallel supercomputer to conduct the computer experiments and also examine methods for improving the computational efficiency. Positron emission tomography (PET) is an emerging technology with unique capability for imaging biochemical processes in the human body. The motivation for this research is that by accounting for scattered photons, the diagnostic and research value of PET data is improved. Scattered photons is a significant problem as 10 to 25 percent of detected photons are deflected from their straight path prior to detection. Moreover, the fraction of photons is even greater, 40 to 50 percent, with the latest generation of PET scanners that use three-dimensional imaging capability to scan the entire body for cancer detection. Even as such, PET is more sensitive for cancer detection and can detect cancer earlier than computed tomography (CT) and magnetic resonance imaging (MRI). PET images can show the vast changes in sugar metabolism associated with cancerous tumors, whereas the tumors must grow to a size sufficent to significantly alter the normal tissue structure in order to be visualized by CT and MRI. More generally, a proper scatter correction will benefit PET's ability to detect and quantify the biochemical changes associated with numerous diseases and particularly those of the heart and brain.
