Dr Jeremy Hebden of University College London (UCL), who is leading the system's development, said it could be tested in hospitals in a year.
An array of detectors picks up how much of the red laser light manages to penetrate the thin bones of the infant skull, and uses that data to reconstruct a picture of how well oxygen is reaching different parts of the brain. That can then be used to plan treatments.
Five per cent of the 14,000 premature babies born in Britain each year suffer birth asphyxia, in which their brains receive insufficient oxygen.
"If you can diagnose that it's happened, you can treat it to prevent permanent damage," said Dr Hebden. "But you can't put them into an X-ray machine or NMR system to see if enough oxygen is getting to the brain."
Cooling the baby to slow brain cell death, or increasing the amount of carbon dioxide in the air it breathes, which encourages blood vessels to expand, are effective treatments.
The system now being built uses components developed to measure neutron flux in nuclear power stations. It arranges 32 light detectors and low- powered laser emitters in a band that would fit around the baby's head.Laser pulses lasting just one picosecond (a thousand billionth of a second) are fired in sequence around the head. Some of the light can penetrate the thinner tissues, some will be absorbed by bone, and some will be absorbed by the blood. But oxygenated tissue and blood absorbs more red light than when deoxygenated, so they will transmit less light.
Simple versions of such systems - which slip over the end of a finger - are already used in many hospitals to measure blood oxygenation levels in adults. The new system is a huge leap forward.
By building up a picture of how different pulses sent to different parts of the skull are absorbed or transmitted to other parts of the skull, and using computerised reconstruction techniques, the scientists can work out how different parts of the brain are coping.
But building up a picture of how well oxygen is reaching tissues within the brain is a very complex problem. "The mathematics are amazingly complex," said Dr Hebden. "There are the bones, and the tissues. You have to make various assumptions about symmetry of the brain. But in the end it should construct a picture of a slice through the skull."Reuse content