Ashya King is undergoing his first tests at a Czech clinic as doctors prepare him for proton treatment.
The five-year-old brain tumour patient has been admitted to the Proton Therapy Centre Czech (PTC) in Prague.
A spokeswoman for the hospital told the Press Association: "He will be undergoing the first MRI examination and a special mask (will be prepared) for his head.
"This will be used for fixing him in the same position during the treatment every day.
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"He will be put asleep before that and he will wake up after noon."
Today's procedures are expected to be completed by around 2pm local time.
Yesterday Ashya finally arrived in the Czech Republic after a protracted legal battle over his care that saw his parents arrested in Spain and separated from him for several days.
Brett and Naghmeh King triggered an international police pursuit when they removed Ashya from Southampton General Hospital on August 28.
They were desperate for him to be given the proton therapy, which was not available to them on the NHS.
Speaking after arriving in Prague, Mr King told Sky News they were "just so happy to be here".
He said: "This is what we wanted from the beginning. Things went from bad to worse at one stage.
"We just want the best for Ashya. He's got to get through this, he's got to get better."
Ashya will undergo tests ahead of the possible proton treatment next week, according to reports.
It is expected to last for around five weeks, with the boy staying at Motol hospital and travelling to PTC each day.