ET ▁sc ans ▁were ▁superior ▁to ▁all ▁other ▁met abol ic ▁imag ing ▁methods ▁in ▁terms ▁of ▁resolution ▁and ▁speed ▁of ▁completion ▁( as ▁little ▁as ▁ 3 0 ▁seconds ), ▁when ▁they ▁first ▁became ▁available . ▁ ▁The ▁improved ▁resolution ▁permitted ▁better ▁study ▁to ▁be ▁made ▁as ▁to ▁the ▁area ▁of ▁the ▁brain ▁activ ated ▁by ▁a ▁particular ▁task . ▁ ▁The ▁biggest ▁draw back ▁of ▁P ET ▁sc anning ▁is ▁that ▁because ▁the ▁radio activity ▁dec ays ▁rapidly , ▁it ▁is ▁limited ▁to ▁monitoring ▁short ▁tasks . ▁ ▁Us es ▁ ▁Before ▁the ▁use ▁of ▁functional ▁magnetic ▁reson ance ▁imag ing ▁( f M RI ) ▁became ▁w ides p read , ▁P ET ▁sc anning ▁was ▁the ▁preferred ▁method ▁of ▁functional ▁( as ▁opposed ▁to ▁struct ural ) ▁brain ▁imag ing , ▁and ▁it ▁still ▁continues ▁to ▁make ▁large ▁contributions ▁to ▁neu ros cience . ▁ ▁P ET ▁sc anning ▁is ▁also ▁useful ▁in ▁P ET - gu ided ▁s tere ot actic ▁surg ery ▁and ▁rad ios urg ery ▁for ▁treatment ▁of ▁int rac ran ial ▁tum ors , ▁ar ter i oven ous ▁mal form ations ▁and ▁other ▁surg ically ▁treat able ▁conditions . ▁ ▁P ET ▁sc anning ▁is ▁also ▁used ▁for ▁diagn osis ▁of ▁brain ▁disease , ▁most ▁not ably ▁because ▁brain ▁tum ors , ▁stro kes , ▁and ▁neur on - dam aging ▁dise ases ▁which ▁cause ▁de ment ia ▁( such ▁as ▁Al z heimer ' s ▁disease ) ▁all ▁cause ▁great ▁changes ▁in