Measurements of overall Wiener spectra in a computed radiography

The 'overall' Wiener spectra of a computed radiographic system (FCR-101) were measured, and compared with the Wiener spectrum of a conventional screen/film system (Hiscreen/RXH). In addition, the noise properties for different exposure conditions to imaging plate (IP), the effects of unsharp masking filter, and the effect of image reduction to output display (film) including the effect of varying the sampling distance were examined. Overall Wiener spectra obtained in the perpendicular direction relative to the laser beam scanning in the laser printer were greater at high spatial frequencies, but comparable at low frequencies than those obtained in the parallel direction, and indicated the existence of a spectral peak around 10 cycles/mm mainly caused by banding artifact. The noise level of the CR system with HR, in the same exposure and gradient relative to the Hiscreen/RXH system, was comparable to that of the Hiscreen/RXH, however the noise level of CR with ST was superior to that of the Hiscreen/RXH. It was also found that the noise level of the CR was increased as the exposure decreased and that the frequency processing (unsharp masking) can increase the CR noise level. Moreover, the noise level was decreased by the effect of the image size reduction. (author)