29679
Confining SPION clusters to such a high level ( 44 wt % ) within the pH - responsive thin gel layer remarkably enhances the transverse relaxivity ( r2 ) and renders the MR imaging highly pH - tunable .
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Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None