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Recently, anatomically shaped lead acrylic filters have been introduced for chest radiography. Two of these filters were compared to several (Al, Cu, Y, and Pb acrylic) uniform filters. Phototimed exposures at 80, 100, 120 and 140 kVp were made on a realistic chest phantom. The optical density in the lung field was kept constant for all filters and kVp's. Exposure time and entrance exposures to the mediastinum and lungs were measured. When compared to standard (3.2 mm Al HVL) aluminum filtration a reduction of (44% - 60%) of lung exposure and better visualization of the mediastinum and retrocardiac areas were noted. However, a significant (80 - 350%) increase in exposure time was required and mediastinum exposure increased by 40 - 100 percent. When using uniform filters, in addition to the standard aluminum filter, entrance exposures to the lung and mediastinum were reduced by 30 -50% for Yttrium and Copper and by 27 to 35% for lead acrylic. Exposure times increased by up to 36%, 64%, and 52% respectively. When using spatially shaped filters, improved image quality and reduced lung exposure results, however, one must be aware of the significant increase in exposure time especially at low (80) kVp's. There is also an increase of medias-tinum exposure and possibility of positioning artifacts.
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