Modern Diagnostic Imaging

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Modern Diagnostic Imaging

• Caterina M. Gallippi, Ph.D.
• Assistant Professor
• Joint Department of Biomedical Engineering

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Why Medical Imaging?
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History of Medical Imaging X-Ray

• 1895 first X-ray, Roentgen
• Static
• Dynamic
• Planar
• 1972 - tomographic X-ray, Hounsfield and Cormack
• Nobel Prize in Medicine, 1979

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History of Medical Imaging Nuclear

• 1896 discovery of radioactivity, Becquerrel
• 1923 radioactive tracers, de Hevesy
• 1937 technetium-99m, Segre and Segre
• 1952 Anger scintillation camera, Anger

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History of Medical Imaging Ultrasound

• 1900 interaction of acoustic waves with media,
  Lord Rayleigh
• WWII Navy Sonar
• 1960s A-mode and B-mode scans
• 1970s Doppler, phased array

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History of Medical Imaging MRI

• 1950s nuclear magnetic resonance, Block and
  Purcell
• 1952 Nobel Prize in Physics
• 1973 application to medicine, Lauterbur
• 2003 Nobel Prize in Medicine, Lauterbut and
  Mansfield

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Ionizing v Non-ionizing

• Ionizing radiation electromagnetic radiation
  whose waves contain energy sufficient to overcome
  the binding energy of electrons in atoms or
  molecules, thus creating ions.
• X-ray
• CT
• Nuclear Imaging

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X-ray

• X-rays transmitted into body by x-ray tube in a
  3-D cone shape
• Tissue selectively attenuates x-ray intensity
• X-ray energy converted to visible light by
  scintillator
• Image captured by photographic film
• Projection Radiography - projection of 3D
  object onto a 2D image

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X-ray Systems
Detector
Emitter
Thoracic
Peripheral
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X-ray Images
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X-ray Images
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Question 1

• Why does bone appear white on the X-ray images?

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Computed Tomography

• Uses x-rays
• Instead of a cone shape, x-rays are collimated
• Large number of small detectors
• Measurements collected for many angular
  orientations
• Image of cross section computed from projections
• Tomographic Image a 2D slice

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CT System
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CT Image
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Question 2

• How can CT be used to generate 3D images?

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CT Images
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How Much is Too Much?
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Nuclear Imaging

• Images can only be made after injection,
  ingestion, or inhalation of radioactive
  substances.
• Radioactive material decays, emitting gamma rays
  or positrons
• Biological carrier to demonstrate biological
  function
• Substances emit gamma rays
• Image reflects local concentration of radiotracer

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Conventional Nuclear Imaging

• Scintigraphy
• Gamma ray detector Anger camera
• Detects single rays, rather than a collective
  beam
• Combines emission with attenuation
• Images 2D projections of 3D distribution of
  radiotracers

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SPECT

• Single-Photon Emission Computed Tomography
• Anger camera rotates
• Computed tomographic methods to reconstruct 2D
  slice
• 3D imaging

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SPECT System
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Fused SPECT/CT
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PET

• Radionuclide decay produces a positron
• Positron electron 2 gamma rays flying in
  opposite directions
• PET scanner identifies coincident detections from
  opposite directions.
• A line of imaging is determined

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PET System
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Pet Images
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Pet Images
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MRI

• Nuclear magnetic resonance in a strong magnetic
  field, the nucleus of a hydrogen atom (a proton)
  tends to align itself with the field.

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MRI

• Results in net magnetization of the body
• Can then selectively excite regions within the
  body to align differently
• As (charged) protons return to alignment, an RF
  signal is generated
• Image created using FT

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Question 3

• Why is the Fourier Transform relevant to image
  creation in MRI?

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MRI System
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Bonus Questions

• Which imaging modality is strictly functional?
• How could you make MRI functional?
• What limitations inhibit clinical applicability?

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Whats Missing?
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cmgallip_at_bme.unc.edu