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1、TISSUE OPTICS Good afternoon, students, today we will talk about knowledge of tissue Optics, and will mainly teach that what is tissue optics and absorption in tissue.,光与组织的相互作用,组织光学光的吸收、散射和透射生物组织的光学特性激光的生物学效应,Outline,What is Tissue OpticsAbsorption in Tissue Absorption Process and ParametersTypical
2、 absorbers in Tissue,What is Tissue Optics?,Definitions from dictionary Optics: a science that deals withgenesis and propagation of light changes that it undergoes and produces Tissue: an aggregate of cells which usually of a particular kind together with their intercellular substance that form one
3、of the structural materials of a plant or an animal,then,What is Tissue Optics? Tissue optics is combination of tissue and optics. Tissue is my subject of interest and optics is my investigating principle.,Tissue,Optics,Investigating Principle,Subject of Interest,+,=,Tissue Optics,Constituents of Ti
4、ssueOptical Properties of TissuePropagation of LightInteraction between Light and TissueDiagnostic and Therapeutic Implications,We are interested in ,Tissue Optics,Optical Signal,Tissue,Light Source,Optical signal will be gained after light through tissue.,Optical Signal from Tissue,Large number of
5、Biological Molecules Functional and Structural information Noninvasive Near real time Optical signal from tissue can gain functional and structural information of large number of biological molecules with noninvasive and real time.,Objectives of Tissue Optics,Key Question: How many photons per secon
6、d will reach the tissue chromophore and be absorbed? Absorption is important because it transfers energy to tissue1. To find the light energy per unit area per unit time that reaches a target chromophore at some position2. To develop methods by the absorption and scattering properties of tissue can
7、be measured,Ultimate Goal of Tissue Optics will be that,Assess all optical properties noninvasive in living tissue (in vivo) We must face Difficulties that Tissue is a complicated heterogeneous system and Requires noninvasive in vivo information for meaningful diagnostic and therapeutic purposes,ABS
8、ORPTION in TISSUE,Absorption,Extraction of energy from light by a molecular species Applications of absorption in tissue as follows Diagnostic applications: Transitions between two energy levels of a molecule that are well defined at specific wavelengths could serve as spectral fingerprint of the mo
9、lecule Various types of Chromophores (light absorbers) in Tissue Wavelength-dependent absorption Tumor detection and other physiological assessments (e.g. pulse-oximetry)Therapeutic applications: Absorption of energy is the primary mechanism that allows light form a source (laser) to produce physica
10、l effects on tissue for treatment purpose Lasik (Laser Assisted in situ Keratomileusis) Eye Surgery, Tatoo Removal, PDT,Mechanism of Absorption (resonance principle),When a light wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational
11、 motion. Just like a tune fork(音叉）!If a light wave of a given frequency strikes a material with electrons having the same vibrational frequencies, then those electrons will absorb the energy of the light wave and transform it into vibrational motion. During its vibrations, the electrons interacts wi
12、th neighboring atoms in such a manner as to convert its vibrational energy into thermal energy. Subsequently, the light wave with that given frequency is absorbed by the object, never again to be released in the form of light. Similar to phonon in crystal lattice conduction of heat in insulators & p
13、roduction of sound in solid,Metrics for Absorption,Absorption Cross-section, s m2 Consider a chromophore idealized as a sphere with a particular geometrical size. Consider that this sphere blocks incident light and casts a shadow, which constitutes absorption. The size of absorption shadow = absorpt
14、ion cross-section,Qa: absorption efficiency,Metrics for Absorption,Pin =IoA,Incident Beam,Pabs = Iosa,Pout = Io(A-sa),Outgoing Beam,area = A - sa,Area = sa,Pout = Io(A-sa),-,=,Area =A,Metrics for Absorption,Assumptions Cross section is independent of relative orientation of the impinging light and a
15、bsorberuniform distribution of identical absorbing particles Absorption Coefficient, ma 1/mAbsorption cross-sectional area per unit volume of medium Absorption mean free path, la mRepresents the average distance a photon travels before being absorbed,Absorption Fundamentals,Transmission and Absorban
16、ce (macroscopic view)TransmissionAbsorbance (attenuation, or optical density),Connection between T/A and ma,Now, absorbing medium is characterized by ma, transmission, and absorbance. Are they related?Lambert Beer Law: the linear relationship between absorbance and concentration of an absorbing species.,Lambert-Beer Law,= absorption cross-sectional area = cm2IO = The intensity entering the sample at z = 0 w/cm2I = The intensity of light leaving the sampleIZ = The intensity entering the infinitesimal slab at ZdI = the intensity absorbed in the slab,
