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We are developing a new method for imaging the human body using light. Near infrared light can pass through about 10cm of tissue, which makes it suitable for imaging the brains of newborn babies and breast cancer. Blood absorbs light strongly and so if we can reconstruct a map showing where light has been absorbed, then we have a map of the distribution of blood. Moreover, blood comes in two colours depending on whether it is carrying oxygen or not. We use two different wavelengths of light to allow us to distinguish between oxygenated and deoxygenated blood.

The near infrared light is generated by a portable fibre laser which delivers pulses at 80 MHz. We have build devices which hold optical connectors comfortably onto the head or breast. We measure the time taken for light to travel across the body and use this data to reconstruct an image. We have used this technique to image the increase in blood volume due to a haemorrhage in the brain, the effect of changing the amount of oxygen in the air supply of a ventilated baby, and the brain's response to passive movement of the arm. We have also imaged about 50 women with breast cancer and detected the increased blood supply around a tumour.