# Optics 1&2- Biomedical imaging

 Give the ways that light can interact with tissuescat Specular reflection, absorption, fluorescence, scattering How does Diffuse optical tomography work in breast scans? DRAW THE DIAGRAM TOO The breast is surrounded by optical sources and sensorsHigh levels of scattering results in banana shaped sensing volumesTomographic reconstruction is still possible and may detect the absorbers in the bloodYou can sense lesions in the breast by detecting increased haemoglobin How does Near infrared spectroscopy of brain activation work Light does not penetrate through tissue but some may be scattered back to the surface Can also study brain activation by detecting absorption at two different wavelengths to detect blood volume Why does scattering occur and give some examples of sources of scattering Occurs due to changes in refractive index eg:Collagen fibrilsMaromolecular aggregatesLysosomesMittochondira NucleiCells Draw the jablonsky diagram What is formula for reduced scattering coefficient? What are the types of scattering? Rayleigh scattering  Mie scattering When does Rayleigh scattering happen? What does the scattering cross section (probaility of scattering) depend on When the wavelength of light is Much larger than the size of particles scattering cross section σ is dependent on λ σ = 1/ λ4 What is the condition of Mie scattering? when wavelength of light is roughly the same as the size of particles What is the formula for mean free path? What is the application of super scattered light like this NIRS brain imagingBreast imaging What is the optical transmission window, and what do you do with it 600-1100nm where haemoglobin absorption is low With this you can take measruements at two wavelengths to see the relative conc of oxy and deoxy haemoglobin Problem: scattering of liight makes accurate measurement difficult What is the application of slightly scattered light like here? Optical tomography but only for thin samples (<10mm). Otherwise not a particularly realistic scenario What is the use for moderately scattered light? (level 3) Useful for photoplethysmography (pulse oximeter)Diffuse optical tomography How does pulse oximetry work Absorption varies depending on the concentration of oxy and deoxy haemoglobin Monitor wavelength at two wavelengths eg 650 and 900nm Since blood volume changes from heartbeat you can filter out the AC component etcCould use it to monitor heartbeat actually. Draw the quantised energy level diagram REMEMBER Y AXIS IS cm-1Also the print is small so the y axis numbers are:1500050001000Then the ones towards the right go down in factors of tenIt goes Electronic,vibrational,Rotational,Translational What kind of light interactions do endoscopes take advantage of? Specular and diffuse reflection Draw a hopkins rod lens endoscope High resWide field of view (100 deg)Wide working range of distancesNot too much chromatic aberration What is narrow band imaging and how does it work? Use narrow bands light instead of full white light spectrum What is formula for quantum efficiency gamma is radiative decay rateK is non radiative decay rate What is formula for fluorescent lifetime gamma is raidative decay rateK is non radiative decay rate What general methods are there to use endoscopes to contrast tissue? White light illuminationNarrow and illuminationFluorescence Authorkeesukim ID340174 Card SetOptics 1&2- Biomedical imaging Descriptionoptics and shit Updated2018-05-13T21:11:36Z Show Answers