MONTE-CARLO STUDY OF GRID PERFORMANCE IN DIAGNOSTIC-RADIOLOGY - TASK-DEPENDENT OPTIMIZATION FOR SCREEN-FILM IMAGING

An optimization of anti-scatter grid design using Monte Carlo techniqu es in diagnostic radiology is presented. The criterion for optimizatio n was to find the combinations of the grid parameters (lead strip widt h, grid ratio and strip density) and tube potential which result in th e lowest mean absorbed dose in the patient at fixed image contrast. Th e optimization was performed in three irradiation geometries, represen ting different scattering conditions (paediatric examinations, and two adult lumbar spine examinations) and was restricted to grids using fi bre materials in covers and interspaces. Grid designs currently availa ble were studied, as were designs which use thinner strips (< 30 mu m) and higher grid ratios (> 18). It was found that grids with widely di fferent strip densities (strips cm(-1)) and grid ratios can have good performance provided that they are used with appropriate strip width a nd tube potential. With increasing amounts of scatter, the optimal gri d requires thicker strips and higher grid ratios. Increasing the strip density and using thinner strips and higher grid ratios are generally required. Grids with low strip density (25 strips cm(-1)) were found to be less sensitive to alterations in strip width. Optimal grids for paediatric radiology require thinner strips (10-20 mu m) than those in currently available grids. Grids on the market are best suited for ex aminations of the adult body in anteroposterior (AP) view. In the adul t lateral view, representing the largest scattering volume, higher gri d ratios (> 18) than those in existing grids would be optimal. Example s of good grid designs are given for each examination.