Chest radiography: optimization of X-ray spectrum for cesium iodide-amorphous silicon flat-panel detector.
OBJECTIVE
To ascertain the optimum x-ray spectrum for chest radiography with a cesium iodide-amorphous silicon flat-panel detector.


METHODS
End points for optimization included the ratio of tissue contrast to bone contrast and a figure of merit (FOM) equal to the square of the signal-to-noise ratio of tissue divided by incident exposure to the patient. Studies were conducted with both computer spectrum modeling and experimental measurement in narrow-beam and full-field exposure conditions for four tissue thicknesses (8-32 cm). Three parameters that affect spectra were considered: the atomic number (Z) of filter material (Z = 13, 26, 29, 42, 50, 56, 64, 74, and 82), kilovoltage (from 50 to 150 kVp), and filter thickness (from 0.25 to 2.00 half-value layer [HVL]).


RESULTS
Computer modeling and narrow-beam experimental data showed similar trends for the full range of parameters evaluated. Spectrum model results showed that copper filtration at 120 kVp or more was optimum for FOM. The ratio of contrasts showed a trend to be higher with higher kilovoltage and only a minor variation with filter material. Full-field experimental results, which reflect the added contribution of x-ray scatter, differed in magnitude but not trends from the narrow-beam data in all cases except the ratio of contrasts in the mediastinum.


CONCLUSIONS
The best performance overall, including both FOM and ratio of contrasts, was at 120 kVp with 1-HVL copper filtration (0.2 mm). With this beam spectrum and an increase in tube output (ie, milliampere seconds) of about 50%, a chest radiograph can be obtained with image quality approximately equal to that with a conventional spectrum but with about 25% less patient exposure.
Dobbins
James T
JT
Department of Radiology, Duke University Medical Center, 161F Bryan Research Bldg, Research Drive, DUMC Box 3302, Durham, NC 27710, USA. jtd@scott.mc.duke.edu
Samei
Ehsan
E
Chotas
Harrell G
HG
Warp
Richard J
RJ
Baydush
Alan H
AH
Floyd
Carey E
CE
Ravin
Carl E
CE
D002586:Cesium; D003198:Computer Simulation; D006801:Humans; D007454:Iodides; D013902:Radiography, Thoracic / Q000379:methods*; D012825:Silicon
D007454:Iodides; D002586:Cesium; C040050:cesium iodide; D012825:Silicon