A computer model of an image intensifier system working under automatic brightness control.

Abstract

A computer model of a fluoroscopy unit operating under automatic brightness control has been developed. The model has been validated by simulating one particular unit but is very general in nature and can easily be applied to other fluoroscopy systems. The model was developed by breaking the operation of a fluoroscopy unit down into its constituent parts then implementing each part in a module of code. It is controlled using the input air kerma to the intensifier face. Discrepancies from the situation when the model is controlled by the energy deposited in the input phosphor have been investigated and shown to be negligible over the operating range. To calculate entrance surface dose rates (ESDRs) to water and polymethylmethacrylate (PMMA) phantoms, Monte Carlo techniques were used to generate backscatter factors for these materials using the beam geometry and range of possible tube potentials and field sizes of a typical mobile image intensifier unit. The model was validated by calculating ESDRs to different thicknesses of water and PMMA phantoms. The predictions generated by the model were in good agreement with experimental measurements. Potential uses of the model include evaluation of dose reduction techniques, investigation of the balance between patient dose and image quality, and assessment of scatter dose.