 This study has two primary objectives. First, we will determine whether the uptake of 11CPS13 in brain and periphery reflects the distribution of COX-1, as demonstrated by blocking with a COX-1 preferential drug aspirin and no effect with a COX-2 selective drug celecoxib. Second, we will measure the testretest reproducibility of brain uptake quantified by compartmental modeling and using arterial blood samples. 