<qa>  What is the name of the new tracer that can be used with?The serotonin transporter SERT regulates the release of sertonin throughout the body. Until recently, radioactive chemicals called tracers were not suitable for viewing SERT activity. However, a newly developed tracer called 11CDASB can be used with positron emission tomography PET imaging to view the parts of the brain that use serotonin. 