Thorax, imaging
For many diagnostic settings conventional X-ray will provide sufficient information with no need for further imaging (e.g. to rule out or to verify pneumonia). The thoracic organs are, however, very complex structures, and CT will provide a lot more information on detail, both regarding to the lung parenchyma and the midline structures, especially when contrast media are used. So, whenever there is any significant doubt in the interpretation of the X-ray pictures, your doctor will order a CT-examination, or in some cases MRI.
Parenchymal lesions; infiltrates and masses
Ordinary X-ray technique has a high sensitivity to detect parenchymal lung-lesions and is indeed able to characterise them correctly in the majority of cases. However, CT is often used to characterise nodular or suspicious mass-like lesions and for further diagnosis of various lung-diseases like fibrosis, emphysema, sarcoidosis and occupational diseases. CT is also useful for guidance when taking biopsies in hospitalised patients.
Evaluation of hilar and mediastinal masses
Both NM (PET), CT and MRI have a high sensitivity to detect pathological masses in these regions compared to ordinary X-ray. To get optimal visibility, CT examinations have to be performed with an injection of contrast media.
MRI is somewhat better to determine the relationship between normal and pathological structures (infiltration, invasiveness of bronchial or vascular linings)
Pleural pathology
Fluid in the pleural space is quite easy to detect both with X-ray, CT and especially ultrasound, which can be done bed-side. None of the modalities, however, can differentiate fluid collections based on inflammatory changes from those caused by malignant processes.
Focal pleural thickening and calcification are best detected with CT.
Pulmonary embolism
Modern, fast CT scanners even have the possibility to detect blood-clots in the pulmonary arteries (pulmonary emboli).
NM has lower sensitivity for centrally located emboli, but is superior for the detection of more distal clots, and is often used for first line screening.
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