Time-gated transillumination of biological tissues and tissuelike phantoms

The applicability and limits of time-resolved transillumination to determine the internal details of biological tissues are investigated by phantom experiments. By means of line scans across a sharp edge, the spatial resolution (Ax) and its dependence on the time-gate width (At) can be determined. Additionally, measurements of completely absorbing bead pairs embedded in a turbid medium demonstrate the physical resolution in a more realistic case. The benefit of time resolution is especially high for a turbid medium with a comparatively small reduced scattering coefficient of approximately pL,' = 0.12 mm-1. Investigations with partially absorbing beads and filled plastic tubes demonstrate the high sensitivity of time-resolving techniques with respect to spatial variations in scattering or absorption coefficients that are due to the embedded disturber. In particular, it is shown that time gating is sensitive to variations in scattering coefficients. Key words: Time-resolved transillumination, turbid media, light scattering, streak camera

Theoretical analysis of transurethral laser-induced thermo-therapy for treatment of benign prostatic hyperplasia. Evaluation of a water-cooled applicator

A mathematical model for predicting the temperature rise in transurethral laser-induced thermo-therapy for benign prostatic hyperplasia was developed. In the model an optical line source emitting light from an Nd:YAG laser isotropically was placed in the urethra. Water cooling of the urethral epithelium was modelled using a two-tube system. The relationship between the difference in outlet and inlet water temperatures and the highest tissue temperature level reached was theoretically investigated. It was found that the water temperature difference was linearly dependent on the steady-state maximum tissue temperature. The theoretical calculations suggest that the water-cooled applicator can be used to measure the maximum tissue temperature. With temperature control, the prostatic tissue temperature can be prevented from exceeding the boiling point of water, excluding tissue carbonization. The model was also used to evaluate the influence of a number of different parameters on the damaged tissue volume. Increasing the urethral lumen radius by a factor of two by means of inserting different sized tubes was found to augment the tissue volume raised to therapeutic temperatures by up to 50%. The calculations showed that cooling of the urethral epithelium can result in an increase in the damaged volume by 80% as compared to not applying any cooling. The temperature of the cooling water was found to influence the tissue temperature only to a small extent

Multibeam fluorescence diffuse optical tomography using upconverting nanoparticles.

Fluorescence diffuse optical tomography (FDOT) is a biomedical imaging modality that can be used for localization and quantification of fluorescent molecules inside turbid media. In this ill-posed problem, the reconstruction quality is directly determined by the amount and quality of the information obtained from the boundary measurements. Regularly, more information can be obtained by increasing the number of excitation positions in an FDOT system. However, the maximum number of excitation positions is limited by the finite size of the excitation beam. In the present work, we demonstrate a method in FDOT to exploit the unique nonlinear power dependence of upconverting nanoparticles to further increase the amount of information in a raster-scanning setup by including excitation with two beams simultaneously. We show that the additional information can be used to obtain more accurate reconstructions