Experimental test of depth dependence of solutions for time

Experimental test of depth dependence of solutions for
time-resolved diffusion equation
Aurélie Laidevant, Anabela da Silva, Michel Berger, Jean-Marc Dinten.
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Leti – Cea Recherche Technologique
Laboratoire Imagerie et Systèmes d’Acquisition
17 rue des Martyrs, 38054 Grenoble Cedex 9, France.
Tel. : +33 4 38 78 25 50
Fax : +33 4 38 78 57 87
E-mail : [email protected]
Poster
Abstract
The determination of optical properties of a semi-infinite medium such as biological tissue
has been widely investigated by many authors. Reflectance formulas can be derived from the
diffusion equation for different boundary conditions at the medium-air interface. This quantity
can be measured at the medium surface.
For realistic objects, such as a mouse, tissue optical properties can only be determined at the
object surface. However, near the surface, the diffusion approximation is weak and boundary
models have to be considered. In order to investigate the validity of the time resolved
reflectance approach at the object boundary, we have estimated optical properties of a liquid
semi-infinite medium by this method for different boundary conditions and different positions
of the fibers beneath the surface.
The time-correlated single photon counting (TCSPC) technique is used to measure the
reflectance curve. Our liquid phantoms are made of water, white paint and Ink. Laser light is
delivered by a pulsed laser diode. Measurements are then fitted to theoretical solutions
expressed as a function of source and detector’s depths and distance.
By taking as reference the optical properties obtained from the infinite model with fibers
deeply immersed, the influence of the different boundary conditions and bias induced are
established for different fibers' depths and a variety of solutions. This influence is analyzed by
comparing evolution of the reflectance models, as well as estimations of absorption and
reduced scattering coefficients.
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Keywords: time-resolved reflectance, diffusion approximation, optical imaging, tissue
optical properties.