Ex vivo clinical measurement of the optical penetration depth in digestive tissues.

The optical penetration depth of 120 biopsy samples taken from normal or neoplastic digestive tissues is measured by means of a device which can be used in a clinical environment, is easy to handle and delivers results quickly. It is seen that, at 655 nm, values of the penetration depth are centred around 1.1 mm and that they can vary by roughly a factor of 2 between samples of a given kind of tissue. This latter result suggests performing individual measurements immediately before carrying out photodynamic therapy.