Preliminary image quality measurements have been performed on a digital photoelectronic imaging system assembled in our laboratory. The system consists of a Gd2O2S:Tb fluorescent screen optically coupled to a microchannel plate (MCP) intensified CCD camera. The imaging system includes a motorized zoom lens, with a zoom range of about 5.2, for changing the imaging field size from 12.0 x 10.7 mm to 63 x 56 mm2. Video images are digitized by a real-time frame grabber integrated with a personal computer for image processing and analysis. The modulation transfer function of the system has been first determined for a 34 x 31 mm2 field size obtaining a spatial resolution limit of about 4.5 lp/mm and of 5 lp/mm in the direction parallel and perpendicular to the TV raster lines. MTF measurements for various zoom factor have been then carried out (only in the perpendicular direction). A spatial resolution limit of about 7.5 lp/mm and 3.5 lp/mm has been obtained for the maximum and the minimum optical zoom factor, respectively. Noise power spectrum analysis has shown that time-invariant noise sources can be removed by a digital background subtraction procedure.
Real-time digital radiography system with variable magnification: MTFs and noise evaluation
GAMBACCINI, Mauro;TAIBI, Angelo;MARZIANI, Michele;
1994
Abstract
Preliminary image quality measurements have been performed on a digital photoelectronic imaging system assembled in our laboratory. The system consists of a Gd2O2S:Tb fluorescent screen optically coupled to a microchannel plate (MCP) intensified CCD camera. The imaging system includes a motorized zoom lens, with a zoom range of about 5.2, for changing the imaging field size from 12.0 x 10.7 mm to 63 x 56 mm2. Video images are digitized by a real-time frame grabber integrated with a personal computer for image processing and analysis. The modulation transfer function of the system has been first determined for a 34 x 31 mm2 field size obtaining a spatial resolution limit of about 4.5 lp/mm and of 5 lp/mm in the direction parallel and perpendicular to the TV raster lines. MTF measurements for various zoom factor have been then carried out (only in the perpendicular direction). A spatial resolution limit of about 7.5 lp/mm and 3.5 lp/mm has been obtained for the maximum and the minimum optical zoom factor, respectively. Noise power spectrum analysis has shown that time-invariant noise sources can be removed by a digital background subtraction procedure.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
