US President Donald Trump says he has had an MRI examination, without saying why.

“It was perfect,” he said on board Air Force One en route to Tokyo on Monday.

A magnetic resonance imaging scan uses magnets and radio waves to create detailed images of the inside of the body. It can be used to monitor a range of conditions.

Trump, 79, was the oldest person to be inaugurated as US president when he retook the White House in January, and he is the second-oldest person to serve in the top job.

Speaking on Air Force One on his way to Japan on Tuesday (AEDT), Trump again did not rule out running for a third term, which is unconstitutional in the US.

“I would love to do it,” he said when asked about a third tilt for the presidency in 2028.

“I have my best numbers ever. It’s very terrible. I have my best numbers.

But Trump said he hadn’t thought about fighting in court for the opportunity. He dismissed the notion of running for vice-president alongside another Republican presidential candidate.

“I’d be allowed to do that,” he said.

“I guess I think it’s too cute. Yeah, I would rule that out because it’s too cute. I think the people wouldn’t like that. It’s too cute. It’s not – it wouldn’t be right.”

Earlier in October, Trump’s doctor said in a medical evaluation that he was in “exceptional health”.

In July, the White House disclosed that Trump was experiencing swelling in his lower legs and bruising on his right hand, after photographs showed him with swollen ankles and makeup covering the afflicted part of his hand.

In a letter released by the White House at the time, Trump’s doctor, Sean Barbabella, said tests had confirmed the leg issue was due to “chronic venous insufficiency” – a benign and common condition, especially in people older than 70.

Barbabella said the bruising on Trump’s hand was consistent with minor soft tissue irritation from frequent hand shaking and aspirin use, which Trump takes as part of a “standard cardiovascular prevention regimen”.

Since then, the White House has played down concerns about Trump’s health, without detailing how the leg issue is being treated.

-with AAP