Organ donors must be declared brain-dead before their organs may be removed for transplant.

器官捐赠者必须在宣布脑死后才可以把他们的器官切除移植。

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About a third of all donated organs are harvested from live donors. Nearly all the rest come from people who have been declared brain dead while undergoing treatment in hospitals.

大约三分之一的器官捐献都是来自活体捐献者，剩下的则基本上来自那些已被宣布脑死亡而又在医院接受治疗的人。

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Researchers at Boston University's Center for the Study of Traumatic Encephalopathy, where Cantu is a co-director, performed a December 2012 study of 85 brain donors who had played football.

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Stefan Duma, a Virginia Tech professor who is studying the issue, said it would be "incorrect" to rely too much on small pools of brain donors whose families may have suspected there was something amiss.

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Japan didn't legalize organ transplants from brain-dead donors until 1997, according to the Japan Organ Transplant Network, a non-governmental group.

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