SelbyTec | Abstract


Figure: SelbyTec Logo
Selby BP, Sakas G, Walter S, Stilla U (2008) Automatic determination of absolute CT coordinates using a table inlay. In: Abstract book of the 20th European Congress of Radiology (ECR).

Automatic determination of absolute CT coordinates using a table inlay

Purpose: CT series can be used to define a reference position for correction of tumor alignment in radio therapeutic cancer treatment by comparison of the projected slices to digital radiographic images. Because the pose of the CT dataset with respect to the table is a priori unknown, a method is introduced that automatically evaluates the placement of a table inlay and generates absolute CT coordinates.
Methods and Materials: CT slices of different sections of a patient on a CT table with an inlay were used to determine the actual table position and pitch angle with respect to a fixed coordinate system. The inlay was designed so that it was possible to unambiguously identify a respective table section by just one single CT slice. Automatic matching of the partly recorded inlay with a given model of the geometry gives the absolute position of the table origin and pitch. Results from manual 3D matching of the model to the inlay were taken as the gold standard.
Results: Comparisons to the manual determination of the table alignment show that the absolute position of the table origin can be found with an accuracy of ±0.5 times the voxel size. The deviation of the pitch value lies within ±0.1°.
Conclusion: Automatic model based matching of a table inlay provides a fast and accurate method to determine absolute CT table coordinates. The method can increase the reliability of alignment correction procedures and offers a practical solution to the problem of the absence of absolute CT coordinates.