ility . ▁A ▁stand ▁or ▁arm ▁can ▁be ▁used ▁to ▁maintain ▁the ▁system ▁on ▁top ▁of ▁the ▁operating ▁field , ▁particularly ▁when ▁the ▁weight ▁and ▁complexity ▁of ▁the ▁device ▁is ▁high ▁( e . g . ▁when ▁multiple ▁cam eras ▁are ▁used ). ▁The ▁main ▁dis adv antage ▁of ▁such ▁devices ▁is ▁that ▁operating ▁the ater ▁lights ▁can ▁inter f ere ▁with ▁the ▁flu ores c ence ▁emission ▁channel , ▁with ▁a ▁consequ ent ▁decrease ▁of ▁signal - to - background ▁ratio . ▁This ▁issue ▁is ▁usually ▁solved ▁by ▁dim ming ▁or ▁switching ▁off ▁the ▁the ater ▁lights ▁during ▁flu ores c ence ▁detection . ▁ ▁F GS ▁can ▁also ▁be ▁performed ▁using ▁minim ally ▁invas ive ▁devices ▁such ▁as ▁la par os cop es ▁or ▁end os cop es . ▁In ▁this ▁case , ▁a ▁system ▁of ▁filters , ▁l enses ▁and ▁cam eras ▁is ▁attached ▁to ▁the ▁end ▁of ▁the ▁pro be . ▁Un like ▁open ▁surg ery , ▁the ▁background ▁from ▁external ▁light ▁sources ▁is ▁reduced . ▁Nevertheless , ▁the ▁exc itation ▁power ▁density ▁at ▁the ▁sample ▁is ▁limited ▁by ▁the ▁low ▁light ▁transmission ▁of ▁the ▁fi ber ▁opt ics ▁in ▁end os cop es ▁and ▁la par os cop es , ▁particularly ▁in ▁the ▁near ▁inf ra red . ▁Moreover , ▁the ▁ability ▁of ▁collect ing ▁light ▁is ▁much ▁reduced ▁compared ▁to ▁standard ▁imag ing ▁l enses ▁used ▁for ▁open ▁surg ery ▁devices . ▁F GS ▁devices ▁can ▁also ▁be ▁implemented ▁for ▁robot ic ▁surg ery ▁( for ▁example