Versatile approximation of the lung field boundaries in chest radiographs in the presence of bacterial pulmonary infections

The most common radiographic manifestation of bacterial pulmonary infections are foci of consolidation which are visible as bright shadows interfering with the interior lung intensity. In critically-ill patients this interference can be severe leading to vague or invisible lung field boundaries which are difficultly distinguished even by experienced physicians. This problem is amplified if the radiographs are of low quality as obtained with a portable x-ray device, routinely used in intensive care units. This paper proposes a pioneering methodology that copes with lung field detection in both stationary and portable chest radiographs by combining statistical grey-level intensity information and directional edge maps. The boundaries of the lung fields are approximated by consecutive intuitively manipulated parametric curves. Conventional and state of the art lung field detection approaches address only stationary radiography, and only a few of them cope with pulmonary infections. The proposed methodology features unsupervised operation, it is not iterative, it is not limited by the patientspsila positioning, and it is tolerant to the presence of consolidations and boundary discontinuities of the lung fields. Its performance is validated on various stationary radiographs and on a set of portable radiographs obtained from patients with bacterial pulmonary infections.