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Lag measurement in an a-Se active matrix flat-panel imager
C Schroeder1, T Stanescu, S Rathee
1Department of Medical Physics, Cross Cancer Institute, University of Alberta, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
Medical Physics
|June 12, 2004
Summary
Lag and residual contrast in amorphous selenium (a-Se) imaging systems are consistently below 1%. These image artifacts primarily depend on the time elapsed after x-ray exposure, not frame rate or radiation dose.
Area of Science:
- Medical Imaging Physics
- Materials Science in Medical Devices
Background:
- Active-matrix flat-panel imagers (AMFPIs) utilizing amorphous selenium (a-Se) are crucial in medical radiography.
- Understanding image artifacts like lag and residual contrast is vital for diagnostic accuracy.
Purpose of the Study:
- To quantify lag and residual contrast in an a-Se AMFPI.
- To investigate the influence of x-ray energy (kV and MV), frame time, and radiation dose on these artifacts.
Main Methods:
- Measurements were performed on an 8.7 cm x 8.7 cm a-Se AMFPI with a 200-microm a-Se layer and 85-microm pixel pitch.
- Lag and residual contrast were assessed for varying frame times, kV and MV x-ray energies, and incident radiation amounts.
- Signal measurements were normalized to the exposure signal to determine lag percentages.
Main Results:
- Lag ranged from 0.45% to 0.91% for the first frame (n=1) and 0.29% to 0.51% for the second frame (n=2) across all energies.
- Residual contrast ranged from 0.41% to 0.75% (n=1) and 0.219% to 0.41% (n=2).
- Lag and residual contrast were found to be dependent on time after exposure, independent of frame time or radiation dose magnitude. MV energies showed slightly less lag than kV energies.
Conclusions:
- Lag and residual contrast in the studied a-Se AMFPI are consistently below 1% for both kV and MV radiographic applications.
- The primary determinant of lag and residual contrast is the time elapsed after x-ray exposure.