Imaging characteristics of the direct and mobile indirect digital radiographic systems

The clinical applications of the current digital radiographic (DR) systems are rapidly growing. With the recent advances in electronic and ubiquitous healthcare systems using digital imaging modalities, the interest of researchers in developing a mobile digital-imaging system for teleradiologic applications in remote areas is growing. These authors recently installed a mobile indirect digital radiographic (IDR) system in their laboratory and conducted this study to evaluate its characteristics. The characteristics of the general direct digital radiographic (DDR) system that was also installed in these authors' laboratory were likewise studied to determine the difference between the two systems. The performances of the two DR systems were evaluated by measuring their modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). For these measurements, two radiographic systems were used; a DR-1000 (TOSHIBA E7239X generator with a Direct Radiography Corp. DR-1000 detector) and an Alpha-R4000 (LISTEM Mobix-1000 generator with a Teleoptic PRA Alpha-R4000 detector). The imaging characteristics of the two systems were measured using the IEC- 61267-defined RQA5 (kVp: 74, additional filtration: 21 mmAl) radiographic condition. The results for the general DDR system, MTF at 10% and DQE values using 1.4 mR at Ocycles/mm were measured as 5.37 cycles/mm and 24%, respectively. The NPS curves were almost constant at the wide range of the spatial frequencies. For the mobile IDR system, MTF at 10% and DQE values using 1.3 mR at Ocycles/mm were measured as 2.4 cycles/mm and 10%, respectively. The NPS curves gradually decreased at frequencies above 0.25 cycles/mm. The DQE of the general DDR system linearly decreased as a function of the spatial frequencies, but that of the mobile IDR system exponentially decreased. The DQEs of the two systems differed significantly at different radiation doses. The results suggested that the actual teleradiologic imaging applications of the mobile IDR system requires further studies in real situations.