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Modular Strip Detector Development Testing for Digital Radiography

Varian is developing a strip detector based on its amorphous silicon (a-Si) technology that will be modular and highly configurable such that it can be used in a wide range of industrial and security imaging applications of various energies and dose levels. The imager will accept both 1D and 2D scintillating arrays and well as standard scintillators. Currently, we are testing a variety of scintillators for comparison that include DRZ+, CsI, CdWO4, and scintillating glass arrays. Preliminary results have been obtained for a polished CdWO4 array with a 1.6 mm pixel pitch, 3 mm thickness, and with 26.5 !m septa separating the pixels. A polished scintillating glass array with 1.176 mm pitch, 3 mm thickness, and 26.5 !m septa has also been tested. The a-Si receptor is a modified 1515DXT-I imager with a standard 127 !m pitch, but will be able to run in excess of 200 frames per second (fps) and in highest resolution mode and at over 600 fps in 2x2 binning mode allowing for imaging to occur on a pulse-to-pulse basis for most accelerators. The module will be designed to be tiled for scaling to large field of view applications. The x-ray source is an HPX 450-11 tube for the kV measurements. Measurements for CNR will be performed per the ASTM E2737 for the different scintillators at 320 kV, 450 kV and in the future at 950 kV. Additionally, contrast improvement will be demonstrated for real-time motion radiography using a shift and stitch time integration technique. For most measurements, unless otherwise noted, the source to object distance (SOD) was 80 cm and the source to imager distance (SID) was 128.6 cm with a geometric magnification of 1.6. Preliminary results at 450 kV with the 1mm focal spot show that the 1.6 mm pitch CdWO4 array can achieve 1-4T sensitivity through 4 inches of steel with a CNR of 5.23, and 1-1T is visible with a CNR of 3.09 with a 180 second exposure. For comparison, 1-4T hole was only barely indicated with 0.91 CNR for a 180 second exposure at the same dose rate for DRZ+. Additional results will be presented and discussed in detail for the other scintillators and energies.

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