Fig. 7 displays images of Cd phantoms (cross and a disk
with 1 mm holes) and ASTM standards (shown in Fig. 6)
obtained with two of the tested samples described in Table
1. Image on the top was acquired with a gadolinium oxide
converter (the structure was deposited on Al with 5 lm of
Gd2O3 bottom layer 35 lm of CsI(Tl) and 5 lm of Gd2O3
top layer) and the image on the bottom was acquired with a
gadolinium fluoride converter (the sensor had 7 lm of
GdF3, 25 lm of CsI(Tl) and a top layer of GdF3 5 lm
thick). The top image displays higher contrast due to the
higher concentration of Gd in the converter layers. Note
the clear graduation of the ‘‘steps’’ as well as the ‘‘gaps’’
in the ASTM phantom. The two ‘‘gaps’’ (white lines running
perpendicular to the varying density of the steps as
seen in the step wedge image) are 250 lm and 130 lm
and can be resolved, showing the spatial resolution and
the contrast sensitivity of the screen.