b. These devices are especially effective where the part or areas to be
examined present widely varying densities, all of which must be satisfactorily
demonstrated on one film. For example, in making the dorsoplanter projection of the
foot (figure 1-8), dorsoplanter or plantodorsal projections of the os calcis, lateral
placentograms, and examinations of the thoracolumbar region are needed. When
normal radiographic techniques are used to demonstrate such parts, it usually happens
that if the thin parts of the subject are properly exposed, the thick parts may be
considerably underexposed. Conversely, gross overexposure of thin parts may occur in
the exposure factors or are adjusted for satisfactory demonstration of the thick parts.
This problem can be corrected by the proper use of the density equalization filters.
Also, the absorbed radiation dosage to the patient is decreased.
c. Filters of this type are sometimes referred to as compensating filters, wedge
filters, differential-absorption filters, supplementary filters, or balancing filters.