Washington DC - President Donald Trump said Monday he had received an MRI scan during a recent hospital visit, providing an explanation for the first time for why he underwent a second medical exam in a year.

The Republican billionaire – who turns 80 in June – has been accused of a lack of transparency over his health, and his surprise trip to Walter Reed medical center on the outskirts of Washington earlier in October fueled further speculation about his physical condition.

"I did. I got an MRI. It was perfect," Trump told reporters aboard Air Force One Monday.

"I gave you the full results. We had an MRI, and the machine, you know, the whole thing, and it was perfect," he added.

MRI – or magnetic resonance imaging – scans are used to diagnose a range of conditions, from tumors, strokes, and multiple sclerosis to much less serious complaints like muscle tears and inflammation.

The White House has not previously offered a reason for the October 10 hospital check-up, which was noted as unusual since presidents typically get only one comprehensive exam a year.

Trump – the oldest person ever inaugurated as US president – declined to say on Monday why he had received the screening, referring reporters to his doctors.

"Nobody has ever given you reports like I gave you. And if I didn't think it was going to be good, either, I would let you know negatively, I wouldn't run, I'd do something," Trump said.

"But the doctor said some of the best reports for the age, some of the best reports they've ever seen."

During his second term, Trump has appeared regularly with bruising on his right hand, sometimes concealed with heavy makeup. The White House said it was linked to the aspirin he takes as part of a "standard" cardiovascular health program.

The administration announced over the summer that the president had been examined for swelling in his legs and diagnosed with chronic venous insufficiency.

The common vein condition – which can also cause cramping and changes in the skin – affects the valves in certain veins, allowing blood to collect, and can be treated with medication or medical procedures.

The administration said at the time of his second check-up that his lab results – including heart screening – were within normal limits, and there were no signs of arterial disease or deep vein thrombosis.

"President Trump continues to demonstrate excellent overall health," his doctor, Navy Captain Sean Barbabella, wrote in a letter released by the White House.