OSA Short Course: Towards deep tissue luminescence imaging using upconverting nanoparticles

Andersson-Engels 2013

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By Prof. Stefan Andersson-Engels

Lund University, Sweden

Abstract

This course aims at introducing the basics of fluorescence techniques for biomedical imaging, and how the signal is influenced by the tissue optical properties. Fluorescence is a very sensitive technique used in many disciplines. It provides a unique potential for biomedical diagnostics, and is today well explored. Here we will focus on two major challenges that remain for fluorescence imaging in biomedical applications: to achieve good sensitivity and specificity to regions located deeply into tissue, and to image those with as high spatial resolution as possible. Light scattering is making the light diffuse, limiting the spatial resolution of measured images. Light absorption in tissue is providing the basis for generating the fluorescence signal, while it restricts the penetration of light limiting the probe volume. Reabsorption of emitted fluorescence often also alters the spectroscopic signature of the fluorescence signal. This makes it challenging to extract the intrinsic fluorescence properties, directly related to the fluorophore concentration; and to obtain sensitivity at depths. In the course we will address techniques to extract the intrinsic fluorescence signal and also methods to provide better depth sensitivity at slightly better spatial resolution. Two issues are in particular important in order to provide good sensitivity at depth: to use excitation and emission wavelengths penetrating deep into tissue, and to be able to efficiently suppress any unspecific background light generated in other regions of the tissue. Especially fluorescence generated superficially in the tissue, being much less attenuated due to the shorter light paths through the tissue, constitute a severely disturbing source of background limiting the sensitivity for deep imaging. Upconverting nanoparticles (UCNPs) provide unique abilities to obtain images of deep tissue locations. They can be engineered so that both the excitation and emission wavelengths are in the tissue optical window (at wavelengths where tissue is attenuating the light as little as possible). They also provide a signal that is shifted towards shorter wavelengths than the excitation, providing very powerful possibilities to completely filter out any tissue autofluorescence, and thus provide a background-free signal. In addition they yield an improved spatial resolution. This is because they require several photons to be sequentially absorbed, altering the sensitivity profiles of the excitation process. Much effort is today devoted to develop this new class of optical contrast agent for bioimaging, and some of the current research directions will be outlined in this course.

Learning objectives

This course will enable you to:

Intended audience

Physicists, engineers, and biomedical scientists who are interested in fluorescence techniques and deep optical imaging in tissue will benefit from this course.

Course level

Intermediate

Course Length

Half-day

Instructor

Stefan Andersson-Engels received the M.Sc. degree in engineering physics and the Ph.D. degree in physics from Lund University, Lund, Sweden, in 1985 and 1990, respectively. He was involved in developing methods for tissue diagnostics based on optical spectroscopic techniques. He was at McMaster University, Hamilton, ON, Canada, for one year, and was involved in tissue optics as well as confocal and two-photon microscopy. In 1993, he joined Lund University as an Assistant Professor, and became an Associate Professor in 1994 and a Full Professor in 1999. He is the author or coauthor of more than 160 articles published in peer reviewed journals. His current research interests include optical spectroscopy for biomedical and pharmaceutical applications as well as interstitial photodynamic therapy of malignant tumors. Prof. Andersson-Engels has been a Co-Organizer of several international conferences including the Gordon Conference on Lasers in Biology and Medicine in 2000, the European Conference on Biomedical Optics in 2003, and a series of biannual international summer schools in biophotonics at the Island Ven in Sweden.

Personnel to contact with:

Instructor: Prof. Stefan Andersson-Engels