Pulmonary embolism is an avoidable cause of death if treated immediately but delays in diagnosis and treatment lead to an increased risk. Computer–assisted image analysis of both unenhanced and contrast–enhanced computed tomography (CT) have proven useful for diagnosis of pulmonary embolism. Dual energy CT provides additional information over the standard single energy scan by generating four–dimensional (4D) data, in our case with 11 energy levels in 3D. In this paper a 4D texture analysis method capable of detecting pulmonary embolism in dual energy CT is presented. The method uses wavelet–based visual words together with an automatic geodesic–based region of interest detection algorithm to characterize the texture properties of each lung lobe. Results show an increase in performance with respect to the single energy CT analysis, as well as an accuracy gain compared to preliminary work on a small dataset.

1. Benefits of Texture Analysis of Dual Energy CT for
Computer–Aided Pulmonary Embolism Detection
A. Foncubierta Rodríguez,
O. Jiménez del Toro, A. Platon, P.A. Poletti, H. Müller,
A. Depeursinge

2. Pulmonary Embolism
• Obstruction of arteries in the lungs
• Unspecific symptoms
• High mortality rates:
– 75% (initial hospital admission)
– 30% (3 years after discharge)
• Delays in diagnosis increase the risk
• But easily treated with anticoagulants
2

3. PE Imaging
Material Attenuation Coefficient vs keV
0.
1
1
1
0
1
0
0
40 50 60 70 80 90 100 110 120 130 140
Photon Energy (keV)
m(E)
(cm2/mg)
Iodine
Water
80 keV
140 keV
Conventional CT images
• Wedge shaped regions
• Heterogeneous attenuation
• Correlation with
vascularization and
ventilation
Dual Energy CT images
• 4D Data
• X,Y,Z
• Energy level
• Different materials: different
attenuations
3

4. Dataset
• 25 patients
• Image resolution
• 0.83mm/voxel
(axial plane)
• 1mm inter-slice distance
• 1.25mm slice thickness
• 11 energy levels
• Manually segmented
lobes
• Qanadli index
4

5. Pipeline
• Automatic regions of interest
• Region-level features: energy of wavelets
• Lobe-level descriptors: Bag of visual words
• One vocabulary per energy level
3D
Analysis
• Histogram of visual words for all energy-
level vocabularies
• Find optimal combination of energy-level
vocabularies
4D data
integration:
5

6. Automatic ROIs
• Saliency-based:
– 3D Difference of
Gaussians
– Multiple scales
– Geodesic regional
extrema
• Data-driven region
shape
• Local to global analysis
of the lobes
6

7. Region-level Features
4 dimensional feature vector per region
Energy
in
Regions
4 scales
3D DoG
7

8. Bag of visual words
• BOVW allows data-driven features:
– Patterns actually occurring in the data
• Vocabularies
– K-means clustering
– 5 to 25 words
– One vocabulary per energy level
– Lobe specific: lobes are not directly comparable
• Each lobe described by 11 histograms of VW
8

9. Evaluation
• Classification based on 1-NN
– Q_i > 0
– Q_i < 0
• Leave One Patient Out
• Combinations:
– From 1 to 11 energy levels
– 5 to 50 visual words per energy level
• Reference: 70 KeV for conventional CT
9

10. Results
Lobe
4D Analysis
Accuracy
Energy levels
Visual
words
Conventional
Accuracy
Lower Right 84% 50+130 KeV 5 52%
Lower Left 84% 100+140 KeV 5 48%
Middle Right 80% 40+50+130+140 Kev 5 52%
Upper Left 76% 40+70+80+90 Kev 25 60%
Upper Right 80% 90+120 KeV 25 56%
10

11. Conclusions
• Using 4D analysis of DECT outperforms
conventional CT: 36% accuracy increase
• Consistent results among all lobes
• Lobe specificities:
– No optimal parameters for all lobes
– Methods need to be optimized per lobe
• Satisfactory results for integration of
automatic ROI detection
11

12. Future work
Larger
database
• Ongoing process
Similarity-
based retrieval
• Qanadli index as
metric
Optimize
BOVW
• Synonyms
12

13. Thanks for your attention!
Questions?
A. Foncubierta-Rodríguez, O. Jiménez del Toro, A. Platon, P.A. Poletti, H.Müller and
A. Depeursinge, Benefits of texture analysis of dual energy CT for computer-
aided pulmonary embolism detection, in: The 35th Annual International Conference
of the IEEE Engineering in Medicine and Biology Society (EMBC 2013), Osaka 2013