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X-Ray Imaging

Add Event to your Calendar Fri., Nov. 13, 2015 3:00 p.m. - Fri., Nov. 13, 2015 4:00 p.m.

Location: CL 317

Abstract: During x-ray imaging some of incident x-rays are scattered within the patient. These scattered x-rays are detrimental to the image quality of x-ray transmission radiography. Anti-scatter grids have been developed for kilovoltage (kV) x-ray imaging but are impractical to use for megavoltage (MV) xray imaging in radiation therapy. A new approach for scatter reduction, a Čerenkov Electronic Portal Imaging Device (CPID), in MV x-ray imaging is introduced and investigated using Geant4 based Monte Carlo simulations. The results of the simulations show that the CPID system is an inherent anti-scatter detector, the first of this kind, for MV x-ray imaging.

The proposed CPID consists of a matrix of silica optical fibres aligned with the incident x-rays and coupled to an active matrix flat panel imager (AMFPI) for image readout. It relies on Čerenkov effect for MV x-ray imaging. Energetic electrons and positrons are produced in the detector by incident MV x-rays, and those with energy greater than the threshold energy required for Čerenkov radiation in the fibre material trigger Čerenkov light along their tracks. The light photons produced in a fibre core and emitted within the acceptance angle of the fibre are guided towards the optically sensitive AMFPI by total internal reflection. The light signal that reaches the AMFPI is dependent on the energy and the incidence angle of the x-rays that interact with the detector. As a result, the CPID is insensitive to lowenergy scattered radiation. Monte Carlo simulations based on Geant4 toolkit have been conducted to evaluate the response of the proposed CPID to scatted x-rays in comparison with that of conventional EPIDs. The CPID is ~50% less sensitive to scattered x-rays than conventional EPIDs at 6 MV. The differential signal to noise ratio is also improved by up to 30% in CPID due to scatter signal reduction alone.

Speaker: Dr. A. Teymurazyan, Department of Physics, University of Regina