Cavities detection in proximal surfaces of pre-molar and molar teeth

In radiology diagnosis, there is the constant preoccupation with optimisation of radiological contrast to obtain the most faithful diagnosis. To achieve this, radiographic noise must be minimised, principally the influence of quantic noise, which is considered the most fundamental in image quality degradation. This can be reduced by increasing the intensity of the X-rays or their exposure time, which would have negative effects on the patient. Methods can be found that optimizes the radiographic signal to noise ratio (S/N) to obtain the best contrast with a quasimonochromatic spectrum that improve the image contrast. Filters in the X-ray beams permit the undesirable photons (those of lower energies) to be removed, minimising the energy to be absorbed and filters with suitably selected rare earths (considering the spectrum of X-rays and the absorption energy of its K-edge) pass a narrow spectrum of X-rays with appropriate energies for the composition and thickness of the object structure. The investigation of these filters in radiology has been published, frequently presenting conflicting results, owing to the choice of filter materials, structure thickness to be studied and individual concept of contrast. In this work, the reduction of quantic noise in radiographs was investigated analytically and experimentally for the detection of cavities, using rare-earth. The resulting spectra were optimized for the detection of cavities of 1 to 2 mm. Radiographs were produced with these spectra and various sizes of cavities, simulated and subsequently evaluated by six dentists. The dentists had no knowledge of the filter materials or techniques employed and they scored the radiographs from 0 to 10. These scores agree with the results obtained analytically. (author)