WE‐E‐18A‐11: Fluoro‐Tomographic Images From Projections of On‐Board Imager (OBI) While Gantry Is Moving

Purpose: A method to generate a series of fluoro‐tomographic images (FTI) of the slice of interest (SOI) from the projection images of the On‐board imager (OBI) while gantry is moving is developed and tested. Methods: Tomographic image via background subtraction, TIBS has been published by our group. TIBS uses a priori anatomical information from a previous CT scan to isolate a SOI from a planar kV image by factoring out the attenuations by tissues outside the SOI (background). We extended the idea to 4D TIBS, which enables to generate from the projection of different gantry angles. A set of background images for different angles are prepared. A background image at a given gantry angle is subtracted from the projection image at the same angle to generate a TIBS image. Then the TIBS image is converted to a reference angle. The 4D TIBS is the set of TIBS that originated from gantry angles other than the reference angle. Projection images of lung patients for CBCT acquisition are used to test the 4D TIBS. Results: Fluoroscopic images of a coronal plane of lung patients are acquired from the CBCT projections at different gantry angles and times. Change of morphology of hilar vessels due to breathing and heart beating are visible in the coronal plane, which are generated from the set of the projection images at gantry angles other than antero‐posterior. Breathing surrogate or sorting process is not needed. Unlike tomosynthesis, FTI from 4D TIBS maintains the independence of each of the projections thereby reveals temporal variations within the SOI. Conclusion: FTI, fluoroscopic imaging of a SOI with x‐ray projections, directly generated from the x‐ray projection images at different gantry angles is tested with a lung case and proven feasible. This technique can be used for on‐line imaging of moving targets. NIH Grant R01CA133539