Military roentgenology / War Department.

Date:
[1944]
Catalogue details

Licence: Public Domain Mark

Credit: Military roentgenology / War Department. Source: Wellcome Collection.

    81/470 page 71
    The grid ratio might be determined by positioning the X-ray tube off center to the extent of the geo- metric base as considered in relation to the similar triangles. (See fig. 70.) For example, if it is thought that the ratio is 5 to 1 and the radius is 30 inches, the geometric relationship would be: 5:1::30:x—indi- cating that a shift of the X-ray tube to the extent of 6 inches should result in a complete cut-off of radiation effect. 89. INTENSIFYING SCREENS. The intensification factor of intensifying screens (par. 123) may be determined by comparing the density of films made with intensifying screens as compared with the den- sity obtained without intensifying screens. This may be accomplished by making simultaneous exposures upon the two films with all factors being constant except time. The exposure should be made at differ- ent kilovoltages ranging from 30 to 90. The films should be processed in fresh developer in accordance with time-temperature development. Densitometric readings are then obtained of each exposed area of the film and these values are plotted for each kilo- voltage so that the comparisons may be made. The figure 7la illustrates the plotting of the intensifying INTENSIFICATION FACTOR AT DENSITY 1.0 FOR MEDIUM SCREENS 27.36 3.0 8 6 4 SCREENS 2 WITHOUT SCREENS > 2.0 a o 8 lw range A 2 pre ey J 80h a eS 8 6 A 2 479 SECONDS 0.0 0 1 2 LOGiig E INTENSIFICATION FACTOR screen densities as compared with the densities ob- tained without intensifying screens made at 70 kyp. At this kilovoltage and a film density of 1.0 the intensification factor is 27.36. A film density of 1.0 is the ideal value to make the foregoing comparison. The factor may be obtained in this manner for each kilovoltage. These values may be plotted and the average intensification factor of a particular type of intensifying screen obtained. (See fig. 71b.) SECTION Ill. TROUBLE ANALYSES; MAINTENANCE AND REPAIR (See also app. IV.) 90. GENERAL. The term, maintenance of X-ray equipment, should not be construed, solely, as meaning repairs to keep the equipment functioning. It should be thought of, primarily, as preventing failures In operation by routme checking, cleaning, and the elimination of improper handling. Before attempting to remedy X-ray equipment difficulties, the approach of the trouble must be systematic and 30 40 60 KVP
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