MTF and DQE Measurements of Mercuric Iodide x-ray Imagers

The high sensitivity of HgI₂ material for X-rays has been demonstrated previously. In this paper the focus is on the MTF (modulation transfer function), NPS (noise power spectra) and DQE (detective quantum efficiency) measurements and on the evaluations of a 13 cm x 13 cm size Hgl₂ (mercuric iodide) coated X-ray imager with 127 mum pixel pitch. The imager was tested with 70 kVp X-ray beam and 21 mm Al filtration. Since a direct imager has no light scattering, a very high 45% MTF value was measured at the Nyquist frequency in comparison to about 16% of a Csl (indirect) detector with the same pixel pitch. Greater than 50% DQE(0) was also measured at a 35 nGy X-ray exposure. The first frame image lag was less than 8% when the imager was run at a 10 fr/s framerate. Some tests were also repeated with a high-energy 6 MeV X-ray source where similarly high MTF values were found. These new results demonstrate that the Hgl₂ X-ray imagers can be used in cine mode, for low dose (fluoroscopic) imaging in medical, industrial and security applications giving low noise and high sensitivity performance. These new Hgl₂ X-ray imagers may also allow decrease in the dose per medical X-ray examination. The result is a universal Hgl₂ imager, which works for both the keV and the MeV energy ranges with excellent resolution.