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To estimate attenuation using cross sectional CT images and scanned projection radiograph (SPR) images in a series of thorax and abdomen phantoms.

Attenuation was quantified in terms of a water cylinder with cross sectional area ofA_w from both the CT and SPR images of abdomen and thorax phantoms, where A_w is the area of a water cylinder that would absorb the same dose as the specified phantom. SPR and axial CT images were acquired using a dual‐source CT scanner operated at 120 kV in single‐source mode. To use the SPR image for estimating A_w, the pixel values of a SPR image were calibrated to physical water attenuation using a series of water phantoms. A_w and the corresponding diameter D_w were calculated using the derived attenuation‐based methods (from either CT or SPR image). A_w was also calculated using only geometrical dimensions of the phantoms (anterior …