MicroComputed Tomography Imaging Systems

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Micro-Computed Tomography Imaging Systems

• Contemporary Topics in Medical Imaging
• Jacqueline Thiesse

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Outline

• Background Significance
• Recent developments in micro-CT
• Volumetric image formation in micro-CT
• Micro-CT use in pulmonary imaging research studies

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Background Significance

• Development of sophisticated clinical imaging
  techniques
• Magnetic resonance imaging
• Computed tomography
• Ultrasound
• Extension of imaging techniques for the research
  setting
• Micro-computed tomography (micro-CT)

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What is a micro-CT?

• Mini-size CT scanner
• How is it useful?
• Uses x-ray to create high resolution data sets
  through a minimally invasive system.
• Sceening small animals for
• Drug discovery
• Cancer detection and monitoring
• Genomics Applications

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Micro-CTs consist of

• A micro-focused x-ray source
• A specimen
• An x-ray to electronic signal converting imaging
  array
• A holder that rotates the specimen within a
  stationary scanner or rotates the scanner around
  the stationary specimen

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How do we get the resolution?

• Micro-focused x-ray source
• High resolution images come from one of three
  methods
• Cone beam
• Optical magnification
• Bragg diffraction

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(Ritman, 2004)
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Commercially available micro-CT scanners
(Ritman, 2004)
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Recent Developments in micro-CT

• Reconstruction Developments
• Speed Optimization
• Improving Contrast
• Synchrotron radiation
• K-edge subtraction
• X-ray phase delay
• X-ray fluorescence

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Reconstruction Developments

• 1981 Feldkamp built scaled down version of a CT
  scanner
• Used Hermans fan beam algorithm to obtain
  volumetric image data
• Feldkamp and Davis modified from fan beam to cone
  beam geometryreduce time
• Helical CT reconstructionnot limited to short
  scans

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Speed Optimization

• Vital when imaging live animals
• Needed to increase throughput when looking at
  genomic studies
• Use high energy x-ray photon energies
• gt 50 keV

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Improving Contrast Synchrotron Radiation

• Electromagnetic radiation emitted by high-energy
  particles when accelerated to relativistic speeds
  in a magnetic field
• With synchrotron based imaging high resolution
  images are produced using the differences in
  refraction and scatter of x-rays that pass
  through tissue.
• Due to the collimation and monochromacity images
  can be recorded at lower doses.
• Attempts have been made to create
  quasi-monochromatic radiation

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Improving Contrast K-edge subtraction

• Based on the fact that every element has its own
  defined x-ray attnuation value
• Must have very narrow spectral bandwidth x-ray to
  use this method
• Trying to utilize quasi-monochromatic radiation

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Improving Contrast X-ray phase delay

• Inherent property that x-rays travel at different
  velocities through different tissue types
• Phase differences are transferred into patterns
  based on x-ray intensities and can be
  mathematically converted to actual phase delays
• 4xs more sensitive than monochromatic
  synchronization photon detector

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Improving Contrast X-ray fluorescence

• Fluorescence created by electron being knocked
  out of orbit by x-ray photon and replaced by a
  falling electron
• Difficult to differentiate the fluorescent
  photons from scattered photons

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Volumetric Image formation in micro-CT

• Feldkamp cone beam reconstruction
• Algorithm consists of three main steps
• Weight the projected data
• Convolve the weighted projections
• Backproject and weight each filtered projection
  over the 3D reconstructed volume

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Volumetric Image formation in micro-CT
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Micro-CT use in pulmonary imaging research studies

• Imaging Mouse Models Emphysema

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Micro-CT use in pulmonary imaging research studies

• Imaging Mouse Models Asthma

Kline, 2003
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Micro-CT use in pulmonary imaging research studies

• Imaging large organ biopsies