[Examination of the constancy of the medium optical density of conventional chest radiographs]

To determine whether the medium optical density of conventional chest radiographs is constant.

47 PA chest radiographs were digitized to measure the optical density and its dynamic range of normal and pathologically altered lungs.

For constant exposure factors and a correctly positioned region of interest, the medium optical density deviates only minimal despite differences in AP chest diameter, entry dose and dynamic range, and is largely independent of the pathologic pulmonary findings.

Digitization of the radiograph enables the determination of the physical parameters used to operate the imaging system, such as medium optical density, image contrast, image latitude and density distribution, in accordance to the guidelines of the German Medical Association. If the region of interest encompasses the clinically relevant region of the lung, the measured value of the optical density corresponds with only minor variation to the average value of the entire lung region.