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medical imaging
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Wim van Aarle .
Small animal imaging with discrete tomography..
08 November 2012
Breakout session on Small Animal Imaging
iMinds the conference 2012
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Computed tomography
CT
reconstruction projection data projection
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CT in biomedical research
Osteoporosis
• “Detecting early bone changes using in vivo micro-CT in ovariectomized, zoledronic acid-treated, and sham-operated rats”, E. Perilli, V. Le, B. Ma, P. Salmon, K. Reynolds, N.L. Fazzalari, Osteoporos. Int (2010) 21:1371-1382.
- 20 female albino rats, divided in 3 groups • OVX: ovariectomized (induces loss of bone strength)
• OVX+ZOL: treated with zolendronic acid
• SHAM: sham-operation (testset)
- Longitudinal study • Week 0, 2, 4, 8, 12
- SkyScan 1076 µCT • FDK reconstructions of ROI
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CT in biomedical research
Osteoporosis
Week 0, OVX+ZOL Week 0, OVX
bone parameter value
BV/TV (%) 2.6
Tb.Th* (µm) 77
Tb.Sp* (µm) 1058
Tb.N (1/mm) 0.35
SMI 2.5
bone parameter value
BV/TV (%) 17.6
Tb.Th* (µm) 74
Tb.Sp* (µm) 255
Tb.N (1/mm) 2.41
SMI 1.9
Week 12, OVX Week 12, OVX+ZOL
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CT in biomedical research
Osteoporosis • A few important issues
- Are the bone parameters correct?
- X-rays are harmful! • Rats are animals too
• Radiation might induce bone changes
• Is it possible to draw similar conclusions with less radiation?
• Possible solution: Discrete tomography
noise, misalignment,
motion, etc.
PVE, beam hardening,
etc.
PVE, limited data,
etc.
threshold selection
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Computed tomography
limited data problem
• Ill-posed reconstruction problem - Many unknown (pixels)
- Few measurements (detectors)
0° 180° 0° 180° 0° 180° 0° 180° full angular data low angle count limited angular range truncated data
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Computed tomography
limited data problem
• Discrete Tomography Discrete Algebraic Reconstruction Technique => DART
• Assumptions - homogeneous objects
- prior knowledge: grey levels
phantom image
reconstruction from
5 projection images
segmentation
difference
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Discrete tomography
DART
iteration 1 error pixels: 9491
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Discrete tomography DART
iteration 10 error pixels: 5460
iteration 1 error pixels: 9491
iteration 50 error pixels: 233
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DART in biomedical research
Osteoporosis
DART can be applied for in-vivo bone reconstructions
- 3 homogeneous materials (air, tissue, bone)
- Prior knowledge can be obtained from a hardware phantom
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DART in biomedical research
Some results Overlay of FDK reconstruction with
- FDK segmentation (underestimated)
- DART reconstruction (slightly overestimated)
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DART in biomedical research
Some results
Trabecular Thickness
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DART in biomedical research Trabecular Separation
Some results
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In conclusion
• Computed Tomography
- is still a popular imaging modality in biomedical research
• Discrete Tomography
- allows accurate reconstructions from limited projection data
- combines segmentation and reconstruction
• Discrete Tomography in small animal imaging
- conclusions can be drawn with less radiation
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The end Thanks!
Special mention:
dr. Egon Perilli, Flinders University, Australia
dr. Elke Van de Casteele, University of Antwerp
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