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Solitary or multiple pulmonary cysts are a relatively rare finding and should always prompt the search for an underlying cause. High-resolution computed tomography (HRCT) plays a crucial role in the differential diagnosis with morphological findings, such as cyst shape and size, wall consistency, number, distribution and localization of the cysts being the important criteria. The differentiation of diseases with multiple, diffusely distributed cysts from diseases with single or grouped cysts facilitates the definition of the final diagnosis. Associated pulmonary findings, such as nodules, ground-glass opacities and fibrosis or pleural changes also play a role. Possible underlying diseases can have systemic, inhalative, traumatic, genetic or infectious causes.

Lung cancer is a histologically, immunologically and therefore morphologically and functionally very heterogeneous group of neoplasms with the highest cancer mortality worldwide. Therefore, the range of diseases mimicking lung cancer is also very broad and includes congenital, infectious and inflammatory changes as well as other benign space-occupying lesions and other primary and secondary pulmonary neoplasms. The difficulty in radiology lies in the ability to diagnose lung cancer with a high degree of certainty. This must take the limits of the specific diagnosis, knowledge of the classical pitfalls and rare entities that can imitate lung cancer into consideration. Narrowing the differential diagnosis requires close interdisciplinary cooperation and consideration of the patient's clinical and medical history. An accurate analysis of the computed tomography (CT) pattern and distribution of the lesions as well as consideration of additional changes and involvement of other organ systems can be the key to the diagnosis. The use of fluorodeoxyglucose positron-emission tomography CT (FDG-PET-CT) is helpful only in a few mimics of lung cancer. The article describes clinical and radiological findings of mimics of lung cancer also pointing out the limitations of CT and PET-CT for the diagnosis.

Chest radiography still represents the most commonly performed X-ray examination because it is readily available, requires low radiation doses and is relatively inexpensive. However, as previously published, many initially undetected lung nodules are retrospectively visible in chest radiographs.The great improvements in detector technology with the increasing dose efficiency and improved contrast resolution provide a better image quality and reduced dose needs.The dual energy acquisition technique and advanced image processing methods (e.g. digital bone subtraction and temporal subtraction) reduce the anatomical background noise by reduction of overlapping structures in chest radiography. Computer-aided detection (CAD) schemes increase the awareness of radiologists for suspicious areas.The advanced image processing methods show clear improvements for the detection of pulmonary lung nodules in chest radiography and strengthen the role of this method in comparison to 3D acquisition techniques, such as computed tomography (CT).Many of these methods will probably be integrated into standard clinical treatment in the near future. Digital software solutions offer advantages as they can be easily incorporated into radiology departments and are often more affordable as compared to hardware solutions.

Der Nachweis subsolider intrapulmonaler Rundherde stellt ein haufiges Problem in der taglichen klinisch-radiologischen Routine dar. Das biologische Verhalten subsolider Rundherde unterscheidet sich wesentlich von soliden intrapulmonalen Rundherden. Das Risiko fur Malignitat ist fur subsolide Rundherde deutlich hoher im Vergleich zu soliden oder reinen Milchglasrundherden. Die Empfehlungen fur das diagnostische Management subsolider Rundherde wurden entsprechend der Wachstumstendenz sowie des Malignitatsrisikos adaptiert. Eine benigne Atiologie ist bei subsoliden Rundherden ebenfalls oft zu finden. Diese weisen haufig in der Verlaufsuntersuchung eine Grosenreduktion auf oder bilden sich spontan zuruck. Daher wird fur viele subsolide Rundherde primar eine kurzfristige Verlaufskontrolle empfohlen. Da sowohl benigne als auch maligne Veranderungen uber einen langen Zeitraum stabil bleiben konnen, wird in weiterer Folge eine jahrliche Kontrolle uber einen langeren, derzeit noch unklaren Zeitraum empfohlen. Subsolide Veranderungen, welche an Grose und/oder Dichte zunehmen bzw. einen soliden Anteil innerhalb eines Milchglasrundherdes entwickeln, sind bis zum Beweis des Gegenteils als malignomsuspekt zu werten und mussen weiter abgeklart werden.

Flat panel detectors are characterized by improved handling and increased dose efficiency. This allows for increasing of work flow efficiency and for reducing the exposure dose by about 50% compared to current systems with a sensitivity of 400. Whether the increased dose efficiency should be used to reduce acquisition dose or to increase image quality in the chest, will be shown by further clinical experience and will be also determined by the subjective preference of the radiologists. The decreased level of image noise opens new perspectives for image processing that way that elaborated multifrequency processing allows for optimizing the display of very small and low contrast structures that was so far limited by overlying image noise. Specialized applications of dual energy subtraction and temporal subtraction will also profit by the new detector technology and will be further driven forward in context with applications such as computed assisted diagnosis even though this is currently not yet broadly applied. Storage phosphor radiography still represents an important alternative technique based on its larger flexibility with respect to equipment configuration, its broader application options in intensive care and emergency radiology and due to economic reasons. These facts are further underlined by the fact that image quality also in storage phosphor radiography could be constantly increased by improving detector technology and image processing and consequently has a high standard.

All three currently commercially available systems for digital radiography of the chest such as the selenium drum, storage phosphor plates and the flat panel direct detector systems provide an excellent image quality that is at least equivalent or superior to that of conventional film. Reasons for that are the continuously improved detective or dose efficiency of the detector systems and an improved image processing. The new direct detector systems have the largest potential for dose reduction while storage phosphor and selenium radiographs are usually obtained with a dose comparable to that of a 400 speed system. Improved image processing algorithms allow for the production of digital images that are adapted to the conventional image characteristics within the lung regions combined with an increased transparency of the high absorption areas such as the retrocardial and retrodiaphragmatic regions.