20840
This study provides a valuable strategy for the design of highly sensitive iron - oxide - based T1 contrast agents with relatively long circulation half - lives ( ~ 50 min ) , efficient tumor passive targeting ( SKOV3 , human ovarian cancer xenograft tumor as a model ) , and the possibility of rapid renal clearance after tumor imaging .
 iron - oxide
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 iron - oxide