Sk. Chen et al., DETECTION OF SMALL DIFFERENCES IN MASS USING A DIRECT DIGITAL DENTAL-X-RAY SYSTEM, Dento-maxillo-facial radiology, 26(1), 1997, pp. 63-66
Objectives: To evaluate experimentally how in direct digital radiograp
hy heterogenous detector response may influence the depiction of small
mass differences. Methods: A step wedge of a bone-simulating resin wa
s imaged at 70 kVp using Radio-VisioGraphy ZHR 32000. Exposure time an
d step wedge position on the detector varied. The pixel values of the
stored images of the step wedge were converted to luminance values of
the displayed images. Results: The relationship between pixel and lumi
nance values was non-linear. The difference in luminance between adjac
ent steps varied with position of step wedge. Regardless of position,
there was an increase in difference of luminance between steps with in
creasing exposure. A greater relative change in luminance was conseque
ntly seen in the thinner parts of the step wedge. The failure to perce
ive individual steps of the wedge in its thicker parts was related to
insufficient relative change in luminance between steps. Conclusions:
The heterogeneous response of the detector resulted in a varying abili
ty to depict small mass changes over the detector area.