Publication

Local optical characterization of biological tissues in vitro and in vivo

1998
EPFL thesis
Abstract

Two methods for measuring the optical properties of tissue, i.e. reduced scattering and absorption coefficient, were developed. The first one was designed for in vitro investigations. It is based on the measurement of the spatially resolved transmittance through a tissue slab (typically 5 mm thick). The second one was designed for local in vivo investigations. It is based on the measurement of the spatially-resolved diffuse reflectance, close to the source (< 2 mm). A sterilizable probe, of diameter of 2.2 mm was realized for measurements in clinic, during surgery or endoscopy. A model of the light propagation in turbid media was developed based on Monte Carlo simulations. It allows us to establish the correspondence between the optical coefficients to the experimental data (spatially-resolved transmittance or reflectance). The influence of the scattering phase function on the reflectance and transmittance was carefully studied. In particular, the role of the first and the second moment of the phase function were shown for short distances measurements (close to one transport mean free path). Similarity relations, taking into account the first and second moment of the phase function were proposed and assessed. The model was tested extensively by measurements on tissue-like phantoms, with known optical properties. Further assessments of the model were performed by comparison with time-resolved measurements. Investigations on human brain, breast and cervix tissues were performed. Tissue structure (i.e. heterogeneities not taken into account by the model) were found to play a significant role in the light propagation. Normal and malignant brain tissue were investigated in vitro, and in vivo during surgery. Significant differences were found between different type of tissues, and were explained in terms of chromophore content (hemoglobin, water) and specific features of scattering properties.

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Ontological neighbourhood
Related concepts (33)
Tissue (biology)
In biology, tissue is a historically derived biological organizational level between cells and a complete organ. A tissue is therefore often thought of as an assembly of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues. The English word "tissue" derives from the French word "tissu", the past participle of the verb tisser, "to weave".
Connective tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme, derived from the mesoderm, the middle embryonic germ layer. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. The three meninges, membranes that envelop the brain and spinal cord, are composed of connective tissue. Most types of connective tissue consists of three main components: elastic and collagen fibers, ground substance, and cells.
In vitro
In vitro (meaning in glass, or in the glass) studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and its subdisciplines are traditionally done in labware such as test tubes, flasks, Petri dishes, and microtiter plates.
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