Effects of x-ray spectra on the DQE of a computed radiography system

The effect of incident x-ray beam quality on the measured detective quantum efficiency (DQE) of a computed radiography system was investigated. The in cident x-ray beams used had peak tube potentials of 70, 95, and 120 kVp, we re filtered with various thicknesses of a "patient equivalent phantom" (PEP ), aluminum, and copper, and provided a consistent exposure to the storage phosphor. For each peak tube potential and filter combination, the one-dime nsional modulation transfer function and noise power spectrum were measured and the square of the incident signal-to-noise ratio was estimated. The sp atial frequency dependent DQE was calculated from these data. The DQE was i ntegrated to provide an overall estimate of the efficiency and frequency re sponse of the computed radiography system for the various x-ray beams. Ther e was found to be a wide range of integral DQE (IDQE) values for the peak t ube potential and filter combinations used. For example, the IDQE ranged fr om 3.0 to 0.9 mm(-2) using the peak tube potential and filter combinations 70 kVp with 5.1 cm PEP and 120 kVp with 30.3 cm PEP, respectively. Finally, peak tube potential and filter combinations 70 kVp with 10.2 cm PEP and 12 0 kVp with 20.2 cm PEP were chosen as standard x-ray beams that will be use d at our facility to measure the DQE of digital radiographic imaging system s for evaluation and acceptance testing. (C) 2001 American Association of P hysicists in Medicine.