'It was perfect': Trump says he underwent an MRI scan

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

"It was perfect," he told reporters 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.

Earlier in October, the US president's doctor said Trump was found to be in "exceptional health" in a medical evaluation.

In July, the White House disclosed that Trump was experiencing swelling in his lower legs and bruising on his right hand, after photographs showed the president