28080
Previous literature with [ ( 3 ) H ] - EMPA suggest that it may be used as an imaging agent for OX2 receptors ; however , brain penetration is known to be modest .
 [ ( 3 ) H ] - EMPA
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 [ ( 3 ) H ] - EMPA