Time-resolved transillumination for medical diagnostics.

A time-gated technique to improve the possibility of localizing spatial differences in absorption when transilluminating a turbid, highly scattering medium, such as human tissue, is demonstrated. When transmitting picosecond laser pulses and detecting photons on the opposite side of the object, the contrast can be strongly enhanced by detecting only the photons with the shortest traveling time. Measurements on a 35-mm-thick tissue phantom with 5-mm-diameter absorbing objects inside are reported with data for a human hand in vivo. Implications for optical mammography (diaphanography) are discussed.