MTF and DQE measurements of mercuric iodide x-ray imagers

The high sensitivity of HgI2 material for x-rays has been demonstrated previously [1, 2]. 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 HgI2 (Mercuric Iodide) coated X-ray imager with 127 mu m 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 CsI (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 HgI2 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 HgI2 x-ray imagers may also allow decrease in the dose per medical x-ray examination. The result is a universal HgI2 imager, which works for both the keV and the MeV energy ranges with excellent resolution.