GRANULARITY OF X-RAY FILM FUNDAMENTAL PROBLEMS OF POWER SPECTRUM MEASUREMENT

• Published in: Shika Hoshasen Vol. 31; no. 2; pp. 59 - 70
• Main Author: YAMADA, Hidehiko
• Format: Journal Article
• Language: Japanese
• Published: Japanese Society for Oral and Maxillofacial Radiology 15.08.1991
• ISSN: 0389-9705; 2185-6311
• DOI: 10.11242/dentalradiology1960.31.59

Since Rossmann (1963), the power spectrum has been used frequently to evaluate the granularity of X-ray film. However, clear explanation has not been given for this power spectrum measurement. The following two methods were used to measure this power spectmum and a basic investigation was performed. The first method involved the commonly used measurement for power spectrum with a microphotometer. The other was the measurement of power spectrum with a newly developed 16k dots×100 lines FFT system using a microscope-television camera system as input device. The films were single-emulsion Kodak EKTASPEED films with emulsion densities (ED) of 0.08, 0.12, 0.14, 0.20, 0.37, 0.55 and 0.87. Since microphotometer input gives a power value dependent on the emulsion density, in the 30 LP/mm or less spatial frequency non-correlative region, higher power value resulted as the emulsion density of the film became higher. By measuring with microscope-television camera input system, the power value in the spatial frequency non-correlative region showed an emulsion density dependence which was characterized by a single peak at emulsion density of 0.20. Conclusions were as follows. 1. A 16k dots×100 lines power spectrum measurement system using a microscope-television camera system was developed. 2. Heretofore, the granularity of film was evaluated from the power spectrum using the power value in the spatial frequency non-correlative region. Since this power spectrum is determined by factors such as the measurement system and the film emulsion density, there were problems with the evaluation thus obtained. 3. A new method for evaluating granularity from the power value in the spatial frequency noncorrelative region through a power spectrum measurment system utilizing a microscope-television camera system as input device was established.