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

Table of Contents Pulmonary Diseases Advantages of MSCT Scanners Evaluation System: Our Approach Preliminary Results Conclusion 02/13/2006 SPIE 2006 Medical Imaging

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) 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Airway Tree Segmentation Trachea detection to automatically provide seed point Region growing using adaptive thresholding until explosion Processing time: ~10 seconds 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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? 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Inner and Outer Diameters From xradient along Xairway axis From Gradient along Yairway axis 02/13/2006 SPIE 2006 Medical Imaging

Inner and Outer Diameters 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Broncho-Arterial Map Selection of terminal branches Color coding of terminal branches upon BA ratio 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Tapering Index Healthy airway lumens taper from the trachea to terminal branches Indicates lack of tapering and its severity 02/13/2006 SPIE 2006 Medical Imaging

Computation of Tapering Index Airway tree segmentation Skeleton computation d(vk) d(vh) d(Si) Si Diameter map computation Diameter along paths 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Tapering Index Display Color coding at terminal branches Color coding indicates lack of tapering along the whole path 02/13/2006 SPIE 2006 Medical Imaging

Interface Demo 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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

Experiment Correlation between Tapering Index and BA ratio For each dilated terminal branch, Is the corresponding path set as dilated ? Visual inspection for confirmation 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Results Patient Number Number of BA dilated Branches Visual Inspection 64 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% 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

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 02/13/2006 SPIE 2006 Medical Imaging

Thank you for your attention ! 02/13/2006 SPIE 2006 Medical Imaging