Received: 1 September 1996 Accepted: 13 November 1996 S. R. Desai ( ) ⋅ D. M. Hansell Department of Radiology, The Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK FAX: + 44 (171) 351 8098 e-mail: s.desai@rbh.nthames.nhs.uk Introduction The lungs respond pathologically in a stereotypical manner to a variety of insults [1]. In 1967, Ashbaugh and colleagues documented their clinical experience of 12 adult patients, all of whom, despite differing precipi- tating events, developed sudden and progressive dysp- noea, refractory hypoxemia, decreased lung compliance and diffuse alveolar infiltrates on chest ra- diographs [2]. Their descriptions gave birth to the term acute respiratory distress syndrome (ARDS). Much of the subsequent interest in the syndrome has focused on its pathophysiology, complications, management and prognosis. This review considers the role of chest radi- ography and computed tomography (CT) in ARDS. The pathology relevant to the imaging and the recent in- sights into the pathophysiology of the syndrome pro- vided by computed tomography (CT) are also discussed. Radiographic considerations: Chest radiography is performed daily in the majority of patients with ARDS in intensive care units (ICUs) and is used to detect supervening complications and monitor progress. Clinically unsuspected abnormalities or pro- gression of previously documented changes have been reported in 15–65 % of ICU patients [3–5], such a wide range between published studies probably reflecting dif- fering concepts of “significant abnormality”. However, even with an optimistic view of the utility of chest radi- ography, the cost effectiveness of performing this inves- tigation with such frequency has so far escaped formal evaluation. The satisfactory imaging of critically ill patients on the ICU poses special problems. Limited patient mobil- ity and co-operation plus difficulties of access due to monitoring equipment often result in radiographs of non-diagnostic quality. The power output of portable units is limited so that longer exposure times are re- quired, resulting in movement artefact. The shorter film-to-focus distance, together with the usual antero- posterior projection necessitated by the supine posture of most ICU patients, causes magnification effects which hamper accurate interpretation of cardiac size. Consistency of film exposure from day-to-day is hard to achieve using standard portable units, making valid comparisons between serial radiographs difficult and sometimes impossible. The advent of digital systems, particularly those using storage phosphor technology, has addressed many of the limitations of conventional film radiography. A review of the basic principles of digital storage phosphor radi- ography [6] is useful in considering the advantages and disadvantages of this relatively new technology. Following transmission of X-rays through the pa- tient, incident energy is trapped in the phosphor plate as a latent image; the plate itself being housed in the same way as conventional film in a cassette. The plate is scanned by a laser light source whereupon the trapped energy is released in the form of light (the phenomenon of photostimulable luminescence). The light emitted has an intensity proportional to the X-ray energy previously absorbed and is detected by a rapid scanning photomul- tiplier tube which follows in the wake of the laser beam. The detected signal is transformed by an analogue-to- digital converter to digital data. The final digital image may be presented in a number of different formats, in- cluding one which resembles conventional film [7–9] (Fig. 1). S. R. Desai D. M. Hansell Lung imaging in the adult respiratory distress syndrome: current practice and new insights Intensive Care Med (1997) 23: 7–15  Springer-Verlag 1997 REVIEW ARTICLE