A statistical approach for image difficulty estimation in x-ray screening using image measurements

ABSTRACT

The relevance of aviation security has increased dramatically at the beginning of this century. One of the most important tasks is the visual inspection of passenger bags using x-ray machines. In this study, we investigated the role of image based factors on human detection of prohibited items in x-ray images. Schwaninger, Hardmeier, and Hofer (2004, 2005) have identified three image based factors: View Difficulty, Superposition and Bag Complexity. This article consists of 4 experiments which lead to the development of a statistical model that is able to predict image difficulty based on these image based factors. Experiment 1 is a replication of earlier findings confirming the relevance of image based factors as defined by Schwaninger et al. (2005) on x-ray detection performance. In Experiment 2, we found significant correlations between human ratings of image based factors and human detection performance. In Experiment 3, we introduced our image measurements and found significant correlations between them and human detection performance. Moreover, significant correlations were found between our image measurements and corresponding human ratings, indicating high perceptual plausibility. In Experiment 4, it was shown using multiple linear regression analysis that our image measurements can predict human performance as well as human ratings can. Applications of a computational model for threat image projection systems and for adaptive computer-based training are discussed.

References

1. Gale, A., Mugglestone, M., Purdy, K., and McClumpha. 2000. Is airport baggage inspection just another medical image? In Medical Imaging: Image Perception and Performance. Progress in Biomedical Optics and Imaging, vol. 1(26), 184--192.
2. Ghylin, K. M., Drury, C. G., and Schwaninger, A. 2006. Two-component model of security inspection: application and findings. In 16th World Congress of Ergonomics, IEA 2006, Maastricht, The Netherlands, July, 10--14.
3. Green, D. M., and Swets, J. A. 1966. In Signal detection theory and psychophysics, New York: Wiley, 187--194.
4. Hardmeier, D., Hofer, F., and Schwaninger, A. 2005. The object recognition test ort - a reliable tool for measuring visual abilities needed in x-ray screening. In IEEE ICCST Proceedings, vol. 39, 189--192.
5. Krupinski, E. A., Berger, W. G., Dallas, W. J., and Roehrig, H. 2003. Searching for nodules: What features attract attention and influence detection? In Academic Radiology, vol. 10(8), 861--868.
6. Liu, X., Gale, A., Purdy, K., and Song, T. 2006. Is that a gun? the influence and features of bags and threat items on detection performace. In Contemporary Ergonomics, Proceedings of the Ergonomic Society, 17--22.
7. Mahfouz, M. R., Hoff, W. A., Komistek, R. D., and Dennis, D. A. 2005. Effect of segmentation errors on 3d-to-2d registration of implant models in x-ray images. In Journal of Biomechanics, vol. 38(2), 229--239.
8. McCarley, J. S., Kramer, A. F., Wickens, C. D., Vidoni, E. D., and Boot, W. R. 2004. Visual skills in airport-security screening. In Psychological Science, vol. 15, 302--306.
9. Schwaninger, A., Hardmeier, D., and Hofer, F. 2004. Measuring visual abilities and visual knowledge of aviation security screeners. In IEEE ICCST Proceedings, vol. 38, 258--264.
10. Schwaninger, A., Hardmeier, D., and Hofer, F. 2005. Aviation security screeners visual abilities & visual knowledge measurement. In IEEE Aerospace and Electronic Systems, vol. 20(6), 29--35.
11. Schwaninger, A., Michel, S., and Bolfing, A. 2005. Towards a model for estimating image difficulty in x-ray screening. In IEEE ICCST Proceedings, vol. 39, 185--188.
12. Schwaninger, A. 2004b. Computer based training: a powerful tool to the enhancement of human factors. In Aviation Security International, FEB/2004, 31--36.
13. Schwaninger, A. 2005b. Increasing efficiency in airport security screening. In WIT Transactions on the Built Environment, vol. 82, 407--416.
14. Schwaninger, A. 2006b. Airport security human factors: From the weakest to the strongest link in airport security screening. In Proceedings of the 4th International Aviation Security Technology Symposium, Washington, D.C., USA, November 27 - December 1, 265--270.
15. Sluser, M., and Paranjape, R. 1999. Model-based probabilistic relaxation segmentation applied to threat detection in airport x-ray imagery. In Proceedings of the 1999 IEEE Canadian Conference on Electrical and Computer Engineering.
16. Ying, Z., Naidu, R., and Crawford, C. R. 2006. Dual energy computed tomography for explosive detection. In Journal of X-Ray Science and Technology, vol. 14(4), 235--256.