Two lateral sensors of the automatic exposure control (AEC)
system of the radiographic unit were selected for producing images
of consistent image density of the grid image. The image dose of
this grid image was measured and selected as the optimum image
density for this pelvis phantom. With the use of a device with
adjustable air gap thickness, a series of non-grid images of the
pelvis with different air gap thicknesses ranging from 0 to 25 cm
were produced. Under the same tube potential of 85 kVp, adjustment
was made to the tube current (mAs) to achieve a consistent
image dose (whichwas monitored by the 6 cm3 ionization chamber
at the level of image receptor of CR/DR) among the non-grid images.
As a result, same film density as the grid image was maintained
in all the non-grid ones. The produced images were sent to a
workstation for storage and for later image evaluation by the assessors
at two high-resolution monitors. The ESD of the tested