Imaging Chain. Imaging Chain. Imaging Chain. 1. Light source. 2. Object interactions. 3. Propagation & Collection: optics (lenses & mirrors)

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1 1. Light source λ [nm] sunset blue sky 2. Object interactions 3. Propagation & Collection: optics (lenses & mirrors) 1

2 Optics: Lenses Objects Images Optics: Mirrors Object Image 4. Detector or Sensor Photographic Emulsion Electronic Sensor (CCD) 2

3 5. Processing 6. Compression / Storage / Transmission 7. Display 3

4 8. Perception Link #1 The Source of Energy : Source All imaging systems require some source of energy. 1. Source 2. Object 3. Collection 4. Detection 5. Processing 6. Compression/storage/transmi ssion 7. Display 8. Perception 4

5 : Source All imaging systems require some source of energy. Most familiar imaging systems use some form of electromagnetic (EM) radiation such as (1) light, (2) X-rays, (3) infrared radiation, or (4) radio waves Other forms of energy are also used, e.g., pressure waves in seismic imaging and ultrasound Radioactive isotopes in PET scans Magnetic fields in MRI Electromagnetic (EM) Radiation Electromagnetic radiation conveys energy from one point in space to another without a medium It is a Transverse Wave It oscillates PERPENDICULAR to the direction of travel Different from sound waves, water waves, slinky waves, which require a medium (air, water) to carry energy Pressure waves may be Transverse or Longitudinal or both Waves are Sinusoids The same sine function you learned about in high school often written as a cosine, which is symmetric with respect to the origin (z = ) f [] z = A [ k z] = A sin k z + cos π 2 5

6 Transverse wave: wavelength f Peak [] z = A cos[ k z] = A cos π z 2 (λ = Greek letter lambda ) λ λ A z A z= Trough Waves Can Move Through Space The wave becomes a function of space AND time to move f[z] f[z,t] z [] z = A cos 2π mν t λ f (ν = Greek letter nu ) Electromagnetic (EM) Spectrum Frequency = How many wave crests go by per unit time rate of oscillation per unit time measured in cycles per second 1 cycle per second = 1 Hertz [Hz] 6

7 Velocity Δ Velocity = z Δ t = z1 z t t 1 Electromagnetic (EM) Spectrum Velocity = rate of change of position Wave at t=t crest at z=z z Wave at t=t 1 > t crest at z=z 1 z Δz Conversion from Wavelength to Frequency Wavelength: λ [meters] (λ = Greek letter lambda ) Frequency: ν [cycles per second = Hz] (ν = Greek letter nu ) Velocity: c [meters per second] m sec = [ m] c ν = λ 1 sec = Hz 7

8 Relation Between λ and ν Longer λ Lower ν Lower frequencies have longer wavelengths Radio waves have very long wavelengths and thus low frequencies Visible light has shorter wavelengths and thus larger frequencies Electromagnetic (EM) Radiation Thus far, we have described electromagnetic radiation as a wave Under some conditions, it is simpler to consider EM radiation as of particles of energy photons Dual nature of EM radiation, described by: Wavelength λ, frequency ν [Hz] Energy E of a single photon, E = hν = h c λ h: Planck s constant: h erg-sec ν [Hz] = oscillation rate of electromagnetic field Shorter λ Larger ν Larger E Photons of light with shorter wavelengths oscillate more rapidly and thus have larger energies!! Why short-wavelength light (e.g., ultraviolet light and X rays) can be bad for you! 8

9 Electromagnetic (EM) Spectrum Cosmic rays Gamma rays Infrared Light Ultraviolet X-rays Microwaves Radio waves Electrical oscillations wavelength (m) [μå X-ray unit Å nm μm mm cm meter kilometer] [nucleus atom bacteria mouse human RIT moon] ν Increases More Energy per Photon 9