Tissue density measurements from digital chest radiographs

An investigation is made of the possibility of obtaining reliable measurements of tissue density from digital chest radiographs. This involves assessment of the repeatability and uniformity of x-ray exposure using microdensitometry of conventional film and estimation of scattered radiation. The range of variation of film density spatially and over time was found to be within 0.03 optical density units (O.D.). Scatter fraction measurements using partial absorbers gave results within, on average, 6% of the conventional measurement and was found to be approximately linearly related to mass/unit area. By correcting for film response and scatter, measurement of a variety of densities of foam rubber was found to correlate well with true density, with an average error of 5%. The estimation of regional lung ventilation from inspiration/expiration radiographs is investigated, using spatial warping techniques to facilitate the identification of corresponding areas of the two radiographs. © 1985 SPIE.