Theoretical considerations for evaluating the degree of random-periodicity of radiographic noise.

Radiographic noise properties have been evaluated using the Wiener spectrum. However, this approach is not appropriate for periodic noise for two reasons. One is that it takes infinite values at the spatial frequencies of periodic noise. The other is that when adopting a numerical integration, it allows unstable values at each spatial frequency, depending on the integral region. Introducing three types of spectra (W(1), W(2), and W(3)) in connection with the Wiener spectrum, we propose a practical approach to evaluation of periodic noise. Radiographic images sometimes contain noise that is not totally random and not perfectly periodic. Therefore, using the Wiener spectrum and the W(1) spectrum, we also propose two factors for evaluation of the degree of random-periodicity of noise containing periodic signals.