Photoacoustic Detection Of Inhomogeneities In Turbid Media

P. GRONDONA; G. BILMES; H. O. DI ROCCO; D. I. IRIARTE; JUAN ANTONIO POMARICO; H. F. RANEA SANDOVAL

Leuven

Conferencia; ICPPP15; 2009

The problem of detection of inhomogeneities under the surface of turbid media has been an active area of research for the last 15 years. In addition of its potential applications in biology and biomedicine, the detection of irregular bodies within materials is also of great importance in monitoring the environment and in quality assessment areas of technology.In highly scattering materials, such as biological tissue, polymers, turbid liquids, or glassy structures, inspection was only possible by means of X-Rays. This method has the disadvantage that in biological tissue it can trigger degenerative processes in the cells. The photoacoustic technique has sufficiently proven its capability of detecting small amounts of absorbing species in different media. It has also been useful in tumor detection meeting with great success. In several works polymers have been used as turbid media simulating tissues, because they are good materials in which to implement the technique.In this work we show that not only photoacoustic techniques can reveal the presence of an object inside a diffusive material: the photoacoustic detection of the inhomogeneities also can be enhanced by excitation of the material by a highly absorbing surface. Parallelepipeds made of Grilon were irradiated with pulsed Nd: YAG lasers at 1.06 mm, and the resulting photoacoustic signals were captured by means of a PZT detector. Diferent experiments are presented. Results with samples prepared with a centered or eccentrical cylindrical cavity of 3 mm of diameter drilled in it, that was alternatively empty or filled with different liquid substances, are shown. The last case allows to study the different signals produced in four different orientations of the inclusion with respect to the excitation and the PZT position.Other experiments were performed on a sample that have the lateral surfaces engraved with rectangular grooves of 0.2 mm depth, filled with thick black paint. This allows the analysis of the signals produced when the laser impinged on a black groove or in a “white” stripe. The acoustic signals are clearly distinguishable, showing an enhancement in the detection of the cavity when excitation is produced in the black grooves. The system is also sensitive to the substance that fills the cavity.