Additional Study Information: We are seeking patients with obsessive-compulsive disorder (OCD) who are currently experiencing symptoms despite current medication treatment to participate in a research study involving brain imaging and treatment. The goal of this study is to examine whether a type of brain imaging called PET imaging can predict how much benefit patients will have in their OCD symptoms from treatment with an anti-inflammatory medication called celecoxib, which is not FDA-approved for this purpose. This study is seeking adults between the ages 18 and 55 years old who have OCD. Eligible participants with OCD will receive a psychological and medical evaluation to determine eligibility for the study. The study involves a positron emission topography (PET) scan, which involves the administration of the experimental radioactive tracer to measure the level of inflammation in the brain, and a magnetic resonance imaging (MRI) scan, followed by treatment with celecoxib. After completing research procedures, participants may be eligible for up to three months of OCD treatment at no cost. If you are interested in participating, please use the following link to fill out our online form and someone will be in touch with you soon: tinyurl.com/columbiaocdstudy.