Spatial frequency components of normal radiographic anatomical features on intraoral computed radiography

Abstract

Cutoff frequency images eliminating radiographic information of high frequency areas were obtained using a low-pass filter in a spatial frequency domain and inverse fast Fourier transform processing. Using these images, the spatial frequency range of the radiographic information necessary for the X-ray diagnosis of normal anatomical structures on intraoral computed radiography was investigated. Normal anatomical structures were evaluated on either gradational enhancement images or frequency-enhanced images, from which the frequency range of 2.0–3.0 cycles/mm had been eliminated. The mean value of spatial frequency components did not differ markedly between the frequency-enhanced images and the gradational enhancement images. However, the evaluations made by different examiners varied less in the case of the frequency-enhanced images. The diagnostic ability demonstrated, with film output images and cathode ray tube (CRT) output images, was within a narrow range. This indicates that images displayed on monitors are as useful diagnostically as conventional dental film images.