Objective To establish a computer simulation system to investigate functional cone - beam CT imaging based on projection data in order to realize on - line biologic image guided radiation therapy. Methods Dynamic contrast enhanced CT (DCE - CT) scanning were performed on rabbit. Computer simulation system was built and the cone - beam CT projection data were obtained by using the program of transferring the fan - beam data to the cone - beam data. The change of time - density of each voxel was modeled as a uniform function. Parameters of this function were resolved by using curve fitting based on the projection data. Finally

functional parameters of rabbit were computed by using existent functional CT (fCT) model. Results Comparing the time - density curve (TDC) from cone - beam CT data in simulation system and the TDC at the same pixel from the original DCE - CT data

good fitting was found at the first increase of TDC and fault fitting was found at the other parts of TDC. Conclusion The functional cone - beam imaging can be implemented based on projection data

and then the perfusion is quantified.