P3‐345: BRAIN STRUCTURAL NETWORK EFFICIENCY IS ASSOCIATED WITH A HIERARCHY OF GRAY MATTER REGIONS: RESULTS FROM THE FRAMINGHAM HEART STUDY. (1st July 2019) - Fletcher, Evan; Seiler, Stephan; Beiser, Alexa S.; Himali, Jayandra J.; Satizabal, Claudia L.; Seshadri, Sudha; Maillard, Pauline; DeCarli, Charlie S.