Skeletal applications for flat-panel versus storage-phosphor radiography: effect of exposure on detection of low-contrast details.
OBJECTIVE
To compare exposure requirements for similar detection performance with flat-panel detectors and the most recent generation of storage-phosphor plates in the simulated scatter of typical skeletal radiographic examinations.


METHODS
A contrast-detail test object was covered with varying thicknesses of acrylic to simulate skeletal exposure conditions in the wrist, knee, and pelvis. Three series were obtained with increasing thicknesses of a simulated soft-tissue layer (5, 10, and 20 cm) and increasing tube voltage (50, 70, and 90 kVp). A fourth series was obtained with exposure conditions adapted to the phantom instructions (75 kVp). Images were acquired with a flat-panel detector (cesium iodide scintillator) and storage-phosphor plates at five exposure levels (speed class range, 100-1,600). Five readers evaluated 84 images to determine the threshold contrast of 12 lesion diameters (range, 0.25-11.1 mm). Statistical significance of differences between the two digital systems was assessed with two-way analysis of variance.


RESULTS
A linear relationship was found between the number of detected lesions and the logarithm of exposure (R(2) > 0.98 for all series). On average, the flat-panel system required 45% less exposure than did the phosphor plates when 20-cm-thick acrylic was superimposed on the test object. Differences in exposure requirements were smaller with decreasing thicknesses of simulated soft-tissue layers and lower tube voltages (39% at 10 cm and 70 kVp, and 17% at 5 cm and 50 kVp). All differences were statistically significant.


CONCLUSIONS
Flat-panel radiography provides improved contrast detectability and a potential for exposure reduction compared with those with storage-phosphor radiography. The best performance was achieved with conditions comparable to those for radiography of the trunk and lowest for conditions that simulate radiography of the extremities.
Uffmann
Martin
M
Department of Radiology, University of Vienna Medical School, Allgemeines Krankenhaus Wien, Waehringer Guertel 18-20, A-1090 Vienna, Austria. martin.uffmann@univie.ac.at
Schaefer-Prokop
Cornelia
C
Neitzel
Ulrich
U
Weber
Michael
M
Herold
Christian J
CJ
Prokop
Mathias
M
D001842:Bone and Bones / Q000000981:diagnostic imaging*; D006801:Humans; D019047:Phantoms, Imaging; D011859:Radiography / Q000379:methods*; D014963:X-Ray Intensifying Screens