Imaging Characteristics of an Amorphous Silicon Flat-Panel Detector for Digital Chest Radiography1
Carey E. Floyd, Jr, PhD,
Richard J. Warp, BS,
James T. Dobbins, III, PhD,
Harrell G. Chotas, MS,
Alan H. Baydush, PhD,
Rene Vargas-Voracek, PhD and
Carl E. Ravin, MD
1 From the Department of Radiology, Digital Imaging Research Division, Duke University Medical Center, Box 3302, Room 139, Bryan Research Building, Durham, NC 27710 (all authors); and the Department of Biomedical Engineering, Duke University, Durham, NC (C.E.F., R.J.W., J.T.D., A.H.B.). Received March 9, 2000; revision requested April 26; revision received May 25; accepted June 15. Address correspondence to H.G.C. (e-mail: harrell.chotas@duke.edu).
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Figure 1a. The FPD used in this study is fabricated as a single panel on a monolithic glass substrate. (a) Amorphous silicon (a-Si) thin-film transistor (TFT) layer is deposited on glass, then overlaid with a structured cesium iodide (CsI) scintillator layer. (b) Side view illustrates the visible light reflector and protective covering that are added.
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Figure 1b. The FPD used in this study is fabricated as a single panel on a monolithic glass substrate. (a) Amorphous silicon (a-Si) thin-film transistor (TFT) layer is deposited on glass, then overlaid with a structured cesium iodide (CsI) scintillator layer. (b) Side view illustrates the visible light reflector and protective covering that are added.
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Figure 2. Linearity of the FPD system response to incident exposure at 120 kVp with 0.5 mm of added copper filtration as measured with and without the grid. SI unit conversion for milliroentgen units, 1 mR = 2.58 x 10-7 C/kg.
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Figure 3. Image uniformity and repeatability. The uniformity of pixel values over the field of view for each of six different images is plotted as the mean of 1,024 measurements of the mean pixel value in nonoverlapping regions of interest. Error bars indicate the SDs. These data demonstrate excellent uniformity and repeatability of mean digital value over time.
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Figure 4. Noise uniformity and repeatability. The uniformity of pixel noise over the field of view for each of six different images is plotted as the mean pixel noise in each of 1,024 nonoverlapping regions of interest. Error bars indicate the SDs. These data demonstrate excellent uniformity and repeatability of regional image noise over time.
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Figure 5. MTF plotted as the presampled (lower curve) and expectation (upper curve) MTFs. The MTF response of the FPD system is superior to that of a storage phosphor CR system (1).
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Figure 6. NPS plotted both as the total NPS and with the fixed-pattern noise removed. Data were measured with 70 kVp, 0.5 mm of added copper filtration, 0.3-mR (8 x 10-8 C/kg) incident exposure, with the grid removed. These curves are virtually identical above about 0.2 cycles per millimeter, indicating little residual structured noise after the pixel-by-pixel calibration procedure.
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Figure 7. DQE plotted for the measurements with residual fixed-pattern noise removed. Data were measured with 70 kVp, 0.5 mm of added copper filtration, 0.3-mR (8 x 10-8 C/kg) incident exposure, with the grid removed. The DQE of the FPD system is more than twice that of a storage phosphor CR system (1).
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Copyright © 2001 by the Radiological Society of North America.
