Optical properties of ex-vivo lung tissue: an integrating sphere approach

Chronic lung infections are among the most diffused human infections, being often associated with multidrug-resistant bacteria. The European project “Light4Lungs” aims at synthesizing and testing an inhalable light source to control lung infections by antimicrobial photoinactivation. To correctly obtain the photokilling action spectrum in vivo [1], the study of light-tissue interaction at the level of the inner airway lumen is paramount. In this context, we measured the optical properties of the lung airways by considering a healthy pig model and an integrating sphere approach [2] (UPB-150-ARTA, Gigahertz). This allowed us to obtain both the total reflectance and transmittance spectra in the visible range, accounting for both the tissue absorption and scattering properties. Fresh pig's lungs (provided by a local butcher) were dissected with a scalpel to obtain bronchi portions which were cut lengthwise and laid inside a glass chamber filled with a buffer solution to keep it hydrated [3]. The incoming light source impinging into the tissue sample consisted in a mercury-vapor lamp (Intensilight® HGFIE, Nikon) coupled to the chamber-sphere system by an optical fiber and collimation optics and producing a ∼50mm2 spot at the sample level. The radiometric measurements were performed by a spectrometer (Avaspec-2048XL, Avantes) which collected light through an optical fiber coupled with the sphere. Preliminary results consisted of reflectance and transmittance spectra of the healthy bronchi lumen tissue in the range λ=300-700 nm and were compatible with the presence of known absorbers such as hemoglobin. The result reproducibility was tested both at the level of the whole methodology on the same sample and by measuring the possible variations between samples coming from different animals. Further measurements will enquire the possible differences with other airway regions from trachea to bronchioles, contemporarily increasing the space resolution of the technique.