medical imaging

1. Small animal imaging with discrete tomography..
Breakout session on Small Animal Imaging
iMinds the conference 2012
Wim van Aarle .
08 November 2012

2. Computed tomography
CT
projection projection data reconstruction
2

3. 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
3

4. CT in biomedical research
Osteoporosis
bone parameter value
Week 0, OVX Week 0, OVX+ZOL BV/TV (%) 17.6
Tb.Th* (µm) 74
Tb.Sp* (µm) 255
Tb.N (1/mm) 2.41
SMI 1.9
bone parameter value
BV/TV (%) 2.6
Tb.Th* (µm) 77
Tb.Sp* (µm) 1058
Week 12, OVX Week 12, OVX+ZOL Tb.N (1/mm) 0.35
SMI 2.5
4

5. CT in biomedical research
• A few important issues
Osteoporosis
- Are the bone parameters correct?
PVE, noise, PVE, threshold
beam hardening, misalignment, limited data, selection
etc. motion, etc.
etc.
- 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
5

6. • Ill-posed reconstruction problem
- Many unknown (pixels) Computed tomography
- Few measurements (detectors) limited data problem
0° 180° 0° 180° 0° 180° 0° 180°
full angular data low angle count limited angular range truncated data
6

7. Computed tomography
limited data problem
• Discrete Tomography
Discrete
phantom image difference Algebraic
Reconstruction
Technique
=> DART
• Assumptions
- homogeneous objects
- prior knowledge: grey levels
reconstruction from segmentation
5 projection images
7

8. Discrete tomography
DART
iteration 1
error pixels: 9491
8

9. Discrete tomography
DART
iteration 1
error pixels: 9491
iteration 10
error pixels: 5460
iteration 50
error pixels: 233
9

10. 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
10

11. DART in biomedical research
Overlay of FDK reconstruction with Some results
- FDK segmentation (underestimated)
- DART reconstruction (slightly overestimated)
11

12. Trabecular Thickness DART in biomedical research
Some results
12

13. Trabecular Separation DART in biomedical research
Some results
13

14. 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
14

15. The end
Thanks!
Special mention:
dr. Egon Perilli, Flinders University, Australia
dr. Elke Van de Casteele, University of Antwerp
15