Biomedical Optics 3 MCQ
40 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the total absorption coefficient of a material composed of multiple chromophores dependent on?

  • The scattering characteristics of the medium
  • The individual extinction coefficients and their concentrations (correct)
  • The energy level of the light photons
  • The thickness of the material only

    • In the context of optical absorption, which term is used to describe the probability that a photon will be absorbed during its travel?

  • Transmission rate
  • Absorption probability (correct)
  • Absorption fraction
  • Photonic retention

    • What phenomenon describes the decrease in light intensity as it travels through an absorbing medium?

  • Radiative loss
  • Light dispersion
  • Optical attenuation (correct)
  • Refractive index reduction

    • What type of scattering occurs when the energy of scattered light remains the same as that of incident light?

    <p>Elastic scattering</p> Signup and view all the answers

    How can concentrations of chromophores in a mixture be determined using spectrophotometry?

    <p>By making measurements at multiple wavelengths</p> Signup and view all the answers

    What can significantly affect the optical properties of biological tissue?

    <p>Optical scattering</p> Signup and view all the answers

    Which of the following accurately describes inelastic scattering?

    <p>Scattered light has a different frequency from incident light</p> Signup and view all the answers

    What is the measurement technique known for evaluating optical absorption spectra?

    <p>Spectrophotometry</p> Signup and view all the answers

    What is NOT a characteristic of elastic scattering?

    <p>Involves a change in wavelength</p> Signup and view all the answers

    What can be implied about a material that has a high total absorption coefficient?

    <p>It absorbs a significant amount of incident light</p> Signup and view all the answers

    What phenomenon causes light to appear to move with a different speed when entering a medium with a different refractive index?

    <p>Wave phase shifting</p> Signup and view all the answers

    What type of scattering is predominant in biological tissues at visible and NIR wavelengths?

    <p>Elastic scattering</p> Signup and view all the answers

    When a photon is reradiated after scattering, how is its energy related to the incoming photon?

    <p>It has equal energy</p> Signup and view all the answers

    What factor causes light to bend when it enters a medium with a different refractive index?

    <p>Speed of light reduction in the medium</p> Signup and view all the answers

    Why does the emitted electromagnetic wave during molecular scattering occur?

    <p>As a result of accelerated charges</p> Signup and view all the answers

    What effect does the accumulation of scattered waves have on the original incoming wave?

    <p>Results in a wave that is phase shifted</p> Signup and view all the answers

    What property of light is altered when it travels through a medium with a different refractive index?

    <p>The direction and speed of propagation change</p> Signup and view all the answers

    In the context of scattering, what mainly affects the speed at which light appears to travel in glass compared to in a vacuum?

    <p>The glass's molecular structure</p> Signup and view all the answers

    What causes light to refract when transitioning between two mediums?

    <p>Change in speed due to variable refractive indices</p> Signup and view all the answers

    What is the result of molecular resonance during scattering?

    <p>Emission of scattered waves at varying frequencies</p> Signup and view all the answers

    What determines the strength of scattering in relation to refractive index fluctuations?

    <p>The relationship between the size of the scatterer and the wavelength of light</p> Signup and view all the answers

    How is the reduced scattering coefficient (µs') mathematically defined?

    <p>µs' = µs(1 - g)</p> Signup and view all the answers

    What does the scattering coefficient (µs) describe in scattering events?

    <p>The mean free path between scattering events</p> Signup and view all the answers

    What does the absorption cross-section represent?

    <p>The power absorbed per unit area to the incident power</p> Signup and view all the answers

    In a collimated beam of light, what happens to the light as it travels through a non-absorbing medium?

    <p>Some light is scattered into various directions</p> Signup and view all the answers

    What is the mean free path in the context of scattering theory?

    <p>The average distance a particle travels between impacts</p> Signup and view all the answers

    How is the molar absorption coefficient calculated?

    <p>By summing the absorption cross-sections of all molecules in one mole of a substance</p> Signup and view all the answers

    What is the purpose of the reduced scattering coefficient (µs')?

    <p>To describe diffusion of photons in a random walk</p> Signup and view all the answers

    What is the unit of measurement for the absorption cross-section?

    <p>Area</p> Signup and view all the answers

    Why is the absorption coefficient of a single molecule not sufficient in tissue optics?

    <p>The behavior of bulk matter composed of multiple molecules needs to be considered</p> Signup and view all the answers

    Which factor contributes to macroscopic scattering?

    <p>Inhomogeneities in the density of scatterers</p> Signup and view all the answers

    What does the term 'optical scattering' relate to in the context of photonics?

    <p>Deflection of light due to particles in a medium</p> Signup and view all the answers

    What characterizes the exponential decay of intensity in a scattered beam of light?

    <p>It is governed by the scattering coefficient</p> Signup and view all the answers

    The scattering process affects light direction in which manner?

    <p>Light is refracted in multiple directions</p> Signup and view all the answers

    What role does Avogadro's number play in determining the molar absorption coefficient?

    <p>It provides the number of molecules in one mole of a substance</p> Signup and view all the answers

    In the random walk of photons, what does each step size represent?

    <p>The inverse of the reduced scattering coefficient</p> Signup and view all the answers

    Which statement about the absorption coefficient as a probability is accurate?

    <p>It relates to the likelihood of energy states transitions</p> Signup and view all the answers

    What is the primary focus of spectrophotometry in this context?

    <p>To measure absorption spectra of substances</p> Signup and view all the answers

    How does transmittance relate to absorbance in spectroscopic measurements?

    <p>Absorbance is the negative logarithm of transmittance</p> Signup and view all the answers

    What is the significance of the scattering coefficient in optical phenomena?

    <p>It quantifies how much light is redirected by a medium</p> Signup and view all the answers

    Study Notes

    Absorption and Scattering

    • The third session of the course covers absorption and scattering topics.
    • Today's session content includes: absorption coefficient, absorption cross-section, molar absorption coefficient, absorption coefficient as a probability, spectrophotometry including measuring absorption spectra, transmittance and absorbance, and spectroscopic inversion.
    • Optical scattering topics discussed are: optical scattering, the physical basis of scattering, molecular scattering refractive index, and scattering coefficient.
    • Absorption coefficient is often given in terms of absorption cross-section.
    • Absorption cross-section is the ratio of the power absorbed by the molecule and the incident Power per unit of area.

    Absorption Coefficient

    • Absorption coefficient is a property for describing the amount of a single molecule absorbing light.
    • In tissue optics, it is necessary to describe the absorption of bulk matter consisting of many molecules.
    • Molar absorption coefficient is obtained by summing up the absorption cross-sections of the molecules in one mole of substance.
    • The mathematical representation of the molar absorption coefficient is α(ν) = ΝΑσ(ν), where ΝΑ = Avogadro's constant, and σ(ν) = absorption cross section.

    Absorption Coefficient as a Probability

    • The probability of a photon being absorbed while travelling a distance δz is μaδz where μa is the absorption coefficient.
    • A plane wave of continuous light irradiating a purely absorbing, non-scattering medium also contributes to this exponential decay.
    • Beer's Law describes the relationship: Φ = Φ0 exp(-μaZ) where Φ0 is the initial intensity of light
    • Spectrophotometry is used to measure optical absorption spectra
    • The intensity will decrease with propagation direction as light is absorbed.

    Measuring Absorption Spectra

    • The measurement of optical absorption spectra is spectrophotometry.
    • Spectrophotometry equation is: IL(λ) = I0(λ) exp(-µa(λ)d) which describes the detected intensity and gives us the coefficient μa(λ) and α(λ).

    Spectroscopic Inversion

    • Given a sample with known chromophores, concentrations of each constituent can be estimated via measurements at different wavelengths.
    • A sample containing multiple chromophores a, b, and c with their respective extinction coefficients εa(λ), εb(λ), εc(λ) can be analyzed.
    • Measurements of absorbance are taken with a spectrophotometer at wavelengths λ1, λ2, λ3.

    Optical Scattering

    • Scattering is often the dominating characteristic in biological tissue.
    • Scattering can be categorized as elastic, where energy is conserved and the scattered light has the same frequency and inelastic, where energy is lost or gained.
    • Elastic scattering is significant in biological tissues with visible and near-infrared wavelengths.
    • The scattering mechanism works because the oscillating dipole (a moving charge) radiates an electromagnetic wave.
    • A photon of equal energy to the incoming photon will be reradiated in a random direction.

    Refractive Index

    • Light travels at a specific velocity in vacuum, and the speed in the glass is c/v.
    • The refractive index is related to why light travels at slower speeds in a glass medium.

    Scattering Coefficient

    • The scattering coefficient (μs) describes the mean free path between scattering events and relates to tissue scattering properties.
    • The reduced scattering coefficient µs' incorporates scattering coefficient μs and anisotropy g. μs' = μs(1−g).
    • The mean free path refers to the average distance travelled by a moving particle (atom, molecule, or photon) between impacts.

    Other Important Concepts

    • Tissue optical properties can be analyzed with reduced scattering coefficient.
    • A g-factor measures forward-peaked light distribution.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Absorption and Scattering PDF

    Description

    This quiz covers crucial concepts in optics, focusing on absorption and scattering. It includes detailed discussions on the absorption coefficient, molar absorption coefficient, and various scattering properties. Test your understanding of how these principles apply in spectrophotometry and tissue optics.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser