Room: Track 1
Purpose: Indirect flat panel detector (I-FPD) performance is limited by the response of their scintillators to single x-rays, i.e. magnitude and variation of gain and blur. Single x-ray imaging is an experimental approach wherein the response of scintillators to single x-rays is recorded using an ultra-high sensitivity camera. We propose a method for measuring spatial-frequency-dependent pulse height spectra (PHS) of scintillators using single x-ray imaging, and using this information to predict MTF(f), NPS(f), and DQE(f) of I-FPDs. The approach is demonstrated using cesium iodide (CsI) samples of various thicknesses and screen-optical properties.
Methods: A sealed source of Am-241 was used to generate ~60 keV ?-rays, which were collimated by a lead pinhole and normally incident on each scintillator sample. Ensembles of single x-ray images (SXIs) were collected by coupling each sample to an image-intensifier optically coupled to an electron multiplying charge coupled device (II-EMCCD). Each SXI was summed in 1D, Fourier transformed, and histogrammed to compute a spatial-frequency-dependent PHS, PHS(f). Scintillator MTF(f), NPS(f), and DQE(f) were calculated directly from the moments of PHS(f). To validate this approach, each sample was also evaluated by direct coupling to a CMOS camera, as in a conventional I-FPD. MTF(f) and NPS(f) were measured using IEC standards, i.e. using a slanted edge and flood field images, respectively. Measurements made using SXI and standard methods were compared.
Results: The shape of PHS(0) agreed with reports in literature, and had well-resolved primary and k-fluorescence escape peaks. Average x-ray-to-light conversion gain was 40 keV-1. MTF measurements made using SXI and standard methods agreed at all spatial-frequencies.
Conclusion: Single x-ray imaging allows the measurement of PHS(f), whose moments may be used to simultaneously predict MTF(f), NPS(f) and DQE(f) of I-FPDs. Additionally, PHS(f) provides the finest granularity metric of intrinsic scintillator performance, and may offer new insight into I-FPD optimization.