1. Automated airway evaluation system for multi-slice computed tomography using airway lumen diameter, airway wall thickness and broncho-arterial ratio
B. L. Odry, A. P. Kiraly, C. L. Novak,
J–F. Lerallut, D. P. Naidich
SPIE Medical Imaging 2006

2. Table of Contents Pulmonary Diseases Advantages of MSCT Scanners
Evaluation System: Our Approach
Preliminary Results
Conclusion
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SPIE 2006 Medical Imaging

3. Pulmonary Diseases
Pulmonary Diseases : Bronchiectasis, asthma, emphysema involve airway abnormalities
Dilatation of airway lumen
Airway wall thickness
Mucus impaction
Airway destruction
For better quantification, measurements are necessary (airway diameter, wall thickness)
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SPIE 2006 Medical Imaging

4. Clinical Evaluation MSCT Scanners
Primary mean to depict such abnormalities
Sub-millimeter resolution throughout the thorax
Isotropic data
Selection of any orientation for airway evaluation
I say “ironic” because all this data is potentially available, yet without automation it is not practical to extract it
Ironically, clinical evaluation today usually involves only a subjective visual inspection
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SPIE 2006 Medical Imaging

5. Our approach Based on airway tree segmentation
Allows easy navigation throughout the 3D volume
Color coding for easy targeting of abnormalities
Measurements of airway lumen, airway walls, broncho-arterial ratio
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SPIE 2006 Medical Imaging

6. Airway Tree Segmentation
Trachea detection to automatically provide seed point
Region growing using adaptive thresholding until explosion
Processing time: ~10 seconds
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7. Airway Tree Parameters
Broncho-Arterial Ratio (1)
measures airway dilatation
Bronchial wall – Arterial Ratio (1)
measures airway wall thickness
Tapering Index
measures proper tapering of airways
(1) “Cystic Fibrosis : Scoring system with Thin-Section CT”, Radiology 1991 Bhalla et al
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SPIE 2006 Medical Imaging

8. Broncho-Arterial Ratio
Healthy airways have a lumen diameter comparable to the adjacent artery’s
Ratio is an indicator of airway dilatation
BA Ratio = Dinner/ DArtery
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SPIE 2006 Medical Imaging

9. Broncho-Arterial Ratio
3D airway measurements
Dual tube segmentation
Inner and outer airway diameters
Average diameter along airway
Artery selection [Odry and al EMBEC 2005]
Using proximity, circularity and orientation similarity
Diameter computation
Technically speaking, why do we need the outer diameter to compute this ratio?
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SPIE 2006 Medical Imaging

10. Airway measurements
3D gradient computation along airway principal axes
Reformatted data by tri-linear interpolation
Cross Section
Region limited by value of maximum diameter
X airway Gradient
Gradient used to detect airway boundaries
Y airway Gradient
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11. Inner and Outer Diameters
From xradient along Xairway axis
From Gradient along Yairway axis
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12. Inner and Outer Diameters
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13. Broncho-Arterial Scoring
Summary of Scoring system of Broncho-Arterial Ratio (1)
Score / Category 1 2 3
Severity of
Dilatation
(ratio)
Absent
(<0)
Mild
(1-2)
Moderate
(2-3)
Severe
(>3)
Color code for
visualization
Green
Yellow
Orange
Red
(1) “Cystic Fibrosis : Scoring system with Thin-Section CT”, Radiology 1991 Bhalla et al
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SPIE 2006 Medical Imaging

14. Broncho-Arterial Map Selection of terminal branches
Color coding of terminal branches upon BA ratio
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15. Airway wall – Artery Ratio
Airway wall thickness decreases with increasing airway generations
Airway walls should not exceed the adjacent artery diameter
Outer / inner diameter difference is used as airway wall thickness
Scoring is similar to Broncho-Arterial Scoring
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SPIE 2006 Medical Imaging

16. Tapering Index
Healthy airway lumens taper from the trachea to terminal branches
Indicates lack of tapering and its severity
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SPIE 2006 Medical Imaging

17. Computation of Tapering Index
Airway tree segmentation
Skeleton computation
d(vk)
d(vh)
d(Si) Si
Diameter map computation
Diameter along paths
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SPIE 2006 Medical Imaging

18. Tapering Index Diameter along airway path
Slope estimation along each quarter of path
linear fitting
minimizing chi square error
Score based upon highest slope along the path
Abnormal Slope
Regular Slope
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SPIE 2006 Medical Imaging

19. Tapering Index Scoring
Summary of Scoring system of Tapering Index
Score / Category 1 2 3
Severity of
Bronchiectasis
(slope)
Absent
<-0.15
Mild
[-0.15 : 0.15]
Moderate
[0.15 : 0.35]
Severe
>0.35
Color code
Green
Yellow
Orange
Red
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SPIE 2006 Medical Imaging

20. Tapering Index Display
Color coding at terminal branches
Color coding indicates lack of tapering along the whole path
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21. Interface Demo
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SPIE 2006 Medical Imaging

22. Experiment
9 high-resolution datasets (16-slice detector machine) from radiology practice
Patients scanned for airway diseases and screening purpose
Calculation of BA ratio and Tapering index
Computation of scores upon BA and Tapering parameters
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SPIE 2006 Medical Imaging

23. Result Comparison Tapering index B-A ratio 02/13/2006
SPIE 2006 Medical Imaging

24. Experiment Correlation between Tapering Index and BA ratio
For each dilated terminal branch,
Is the corresponding path set as dilated ?
Visual inspection for confirmation
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25. Correlation BA Ratio-Tapering Index
Results
Patient Number
Number of
BA-dilated Branches
Correlation BA Ratio-Tapering Index
Patient 1 64
0.58
Patient 2 48
0.63
Patient 3 51
0.53
Patient 4 52
Patient 5 25
1.00
Patient 6 33
0.75
Patient 7 36
0.59
Patient 8 43
0.68
Healthy Patient 14
0.79
Average
40.6
Standard
Deviation
15.3
0.14
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SPIE 2006 Medical Imaging

26. Results Patient Number Number of BA dilated Branches Visual Inspection64
78%
Patient 2 48
82%
Patient 3 51
75%
Patient 4 52
80%
Patient 5 25
100%
Patient 6 33
76%
Patient 7 36
91%
Patient 8 43
79%
Healthy Patient 14
85%
Average
40.6
83%
Standard
Deviation
15.3 8%
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SPIE 2006 Medical Imaging

27. Overall, system is able to detect early or subtle abnormalities
Discussion
Visual inspection confirmed good accuracy of method
Tapering index and BA ratio correlation could be improved by better calibration of tapering index
Patients were presented with mild bronchiectasis and no or slight increase of wall thickness
No scoring for airway wall thickness
Overall, system is able to detect early or subtle abnormalities
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SPIE 2006 Medical Imaging

28. Conclusion Global assessment of airways
3D visualization for abnormality localization and extent
3 features for a quantitative global score of airway tree
Reproducible longitudinal assessment of disease severity
Preliminary tests are promising, showing good correlation between features
Approach could be of considerable clinical value in assessment of patients with diffuse airway diseases
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SPIE 2006 Medical Imaging

29. Thank you for your attention !
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SPIE 2006 Medical Imaging