Optimal wavelengths for optoacoustic measurements of blood oxygen saturation in biological tissues.

The non-invasive measurement of blood oxygen saturation in blood vessels is a promising clinical application of optoacoustic imaging. Nevertheless, precise optoacoustic measurements of blood oxygen saturation are limited because of the complexities of calculating the spatial distribution of the optical fluence. In the paper error in the determination of blood oxygen saturation, associated with the use of approximate methods of optical fluence evaluation within the blood vessel, was investigated for optoacoustic measurements at two wavelengths. The method takes into account both acoustic pressure noise and the error in determined values of the optical scattering and absorption coefficients used for the calculation of the fluence. It is shown that, in conditions of an unknown (or partially known) spatial distribution of fluence at depths of 2 to 8 mm, minimal error in the determination of blood oxygen saturation is achieved at wavelengths of 658 ± 40 nm and 1069 ± 40 nm.

Fluorescence diffuse tomography for detection of red fluorescent protein expressed tumors in small animals.

A fluorescence diffuse tomography (FDT) setup for monitoring tumor growth in small animals has been created. In this setup an animal is scanned in the transilluminative configuration by a single source and detector pair. To remove stray light in the detection system, we used a combination of interferometric and absorption filters. To reduce the scanning time, an experimental animal was scanned using the following algorithm: (1) large-step scanning to obtain a general view of the animal (source and detector move synchronously); (2) selection of the fluorescing region; and (3) small-step scanning of the selected region and different relative shifts between the source and detector to obtain sufficient information for 3D reconstruction. We created a reconstruction algorithm based on the Holder norm to estimate the fluorophore distribution. This algorithm converges to the solution with a minimum number of fluorescing zones. The use of tumor cell lines transfected with fluorescent proteins allowed us to conduct intravital monitoring studies. Cell lines of human melanomas Mel-P, Mel-Ibr, Mel-Kor, and human embryonic kidney HEK293 Phoenix were transfected with DsRed-Express and Turbo-RFP genes. The emission of red fluorescent proteins (RFPs) in the long-wave optical range permits detection of deep-seated tumors. In vivo experiments were conducted immediately after subcutaneous injection of fluorescing cells into small animals.