The Reduction of Scatter Fog in Chest Radiography

Generalised fog and the blurring of detail due to scattered radiation in chest radiography is not a major problem when low kilovoltages, low filtration and slow film-screen combinations are used: for this reason few workers routinely employ anti-scatter grids. When higher kilovoltages and faster film, screens, and developer combinations are used, either to reduce exposure time or together with increased filtration to reduce patient dose, resulting films tend to be of low contrast and also often lose detail. When we evolved a technique for low dose chest radiography (Ardran and Crooks, 1952) we attempted to use 90 kVp for all chests: this was a higher kVp than was customarily employed at that time (Ministry of Health Report 1952, Memo. 323/Med.) We had noted that when employing an enlargement technique the contrast of the films was considerably improved and this showed that the use of a higher kVp did not necessarily unduly reduce contrast or detail provided the scatter was removed. It was found that an air gap of about 6 in. between patient and the film was approximately equivalent to a stationary grid in removing scatter.