Frequency Domain Photon Migration Technique Research Articles

Volume of pharmaceutical powders probed by frequency-domain photon migration measurements of multiply scattered light.

Using probability distribution analysis to describe the propagation of multiply scattered light between a point source and point detector located a known distance apart, mathematical expressions predicting the volume of sampled powder were determined for infinite and semi-infinite powder beds and then compared to experimental measurements of frequency-domain photon migration (FDPM). Our results show that the volume of powder sampled varies with optical properties and, when using FDPM techniques, with modulation frequency. For a typical measurement in lactose powder, the volume of powder sampled by multiply scattered light propagating between a 1000-microm-diameter point source and point detector pair separated by 8 mm is predicted to be 1.8 and 1.5 cm3 at modulated frequencies of 50 and 100 MHz, respectively. Experimental measurements in lactose powder confirm the predictions.

Quantitative near-infrared spectroscopy of cervical dysplasia in vivo.

The aims of this study were: (i) to quantify near-infrared optical properties of normal cervical tissues and high-grade squamous intra-epithelial lesions (H-SIL); (ii) to assess the feasibility of differentiating normal cervical tissues from H-SIL on the basis of these properties; and (iii) to determine how cervical tissue optical properties change following photodynamic therapy (PDT) of H-SIL in vivo. Using the frequency domain photon migration technique, non-invasive measurements of normal and dysplastic ecto-cervical tissue optical properties, i.e. absorption (mu(a)) and effective scattering coefficients, and physiological parameters, i.e. tissue water and haemoglobin concentration, percentage oxygen saturation (%SO(2)), were performed on 10 patients scheduled for PDT of histologically-proven H-SIL. Cervix absorption and effective scattering parameters were up to 15% lower in H-SIL sites compared with normal cervical tissue for all wavelengths studied (674, 811, 849, 956 nm). Following PDT, all mu(a) values increased significantly, due to elevated tissue blood and water content associated with PDT-induced hyperaemia and oedema. Tissue total haemoglobin concentration ([TotHb]) and arterio-venous oxygen saturation measured in H-SIL sites were lower than normal sites ([TotHb]: 88.6 +/- 35.8 micromol/l versus 124.7 +/- 22.6 micromol/l; %SO(2): 76.5 +/- 14.7% versus 84.9 +/- 3.4%).