scientists are exploring the possibility of using visible light to gain very clear images of the human body. At present, medical practitioners use diagnostic tools such as magnetic resonance imaging ( mri ), computerised axial tomography ( cat ), positron emission tomography ( pet ) and ultrasonography. With further improvements of optical techniques, a domain of medical imaging may emerge that would provide a way for safe and portable diagnostics ( Science , Vol 276, No 5320).

When a beam of light is exposed on the body, more than 99.9 per cent of the light is absorbed by the molecules or suffers multiple scattering from the cells, whereas a fraction of the light passes through the body. Scientists are developing a technique to use those fractions of light known as