Only months earlier, he had joined the air force. Motivated by a dream to work on helicopters as an airframe fitter, active service had never seemed a likely scenario.

The Hungarian Revolution was contained to 1956, so Bill was off the hook. But come April 1970, there he was, in uniform and on the ground in Vietnam.

He went for two reasons. First, a colleague who was promoted to corporal alongside him confided that his wife had threatened divorce if he went to Vietnam. So, to help take the heat off his friend, Bill also volunteered.

A pragmatist, Bill also thought that by going to Vietnam, he would get a war service loan, which would help his young family buy a house and make a better start in life.

He was there 11 months. But when pounding mounds of waste at a rubbish dump with machine gun fire to use up unwanted ammunition, something exploded. Within seconds, shrapnel was embedded in his arms and face.

The worst, though, was seeing a man accidentally kill himself when his gun fired, sending a bullet through his jaw and into his skull. It haunted Bill. That man was his close friend.

The mental scars are still evident today, flaring up unannounced as panic attacks or festering in frustration.

Bill's wife Maria remembers her husband returning from the war a changed man. He had a shorter fuse and a longer gaze.

"By the time I'm 31, I'm a totally different person," Bill says.

He admits he was in denial for a decade and just "switched off". Between 1971 and 1995, he doubts he spoke to another Vietnam veteran.

Then, in 1995, distracted while following a white ball around a golf course, someone asked him what pension he was on.

" 'Just com super,' I said. And he said, 'No, what pension are you on?' "

From there, Bill slowly returned to circulation. He volunteered with the Gippsland Veterans Welfare Centre in Sale as a pensions officer.

But it was not until 1997 that he was diagnosed with post-traumatic stress disorder.

Now aged 75, Bill has again volunteered. This time for a study into whether there is a link between traumatic brain injury, or PTSD, and Alzheimer's disease. Researchers think there might be.

PTSD expert Malcolm Hopwood, a Florey Institute honorary professor and director of brain disorders program and veterans' psychiatry at the Austin, said it was a new area of research.

"We think that the traumatic memories that are at the core of PTSD result in brain change. They act in a destructive manner in the brain because they are so overwhelming," he says.

Long-term PTSD is already associated with greater risk of heart disease, poorer physical health care and increased smoking, alcohol and drug abuse.

However, the long-term effects on the brain are less understood. Short-term, research has established PTSD can alter the wiring of the brain in areas associated with memory, planning, judgment and concentration.

"One of the common symptoms of Alzheimer's disease is memory disturbance ... and this occurs in the same region of the brain that has disturbed function from PTSD, so there is reason to think that there might be a link," Professor Hopwood says.

Uniting researchers from the Florey Institute of Neuroscience and Mental Health, Austin Health and Melbourne University, the study is being funded with $US750,000 ($827,000) from the US Defence Department.

Alzheimer's disease is characterised by a build-up in the brain of a protein called amyloid.

Neurologist and director of nuclear medicine and PET research at Austin Health, Christopher Rowe, says 150 volunteers will have brain scans, using a technique to highlight the location of amyloid plaques on the brain. Veterans with PTSD will have their scan results compared with veterans without PTSD and veterans who experienced head trauma.

He says findings of the three-year study could have broader relevance, not only for veterans from more recent conflicts but for sports people who have experienced repeat concussions.

Interested in participating in the study? Contact Tia Cummins on 9496 5748 or tia.cummins@austin.org.au.