By combining helical volumetric CT acquisition and thin collimation, CT has gained greater advantages by circumventing the limitations of HRCT, particularly the risk of missing bronchiectasis strictly localised within the intervals between slices. At the present time, multidetector CT with thin collimation is the highly recommended technique to assess the presence and extent of bronchiectasis. Multiplanar reformations increase the detection rate and the reader's confidence, as to the distribution of bronchiectasis, and improve agreement between observers, as to the diagnosis of bronchiectasis. In addition maximum intensity projections improve the detection and display of both mucoid impactions and small centrilobular and linear branching opacities (treein-bud sign), characteristic of infectious bronchiolitis.

The reliability of CT for distinguishing among the causes of bronchiectasis is somewhat controversial. An underlying cause for bronchiectasis is found in fewer than half of patients and CT features alone do not usually allow a confident distinction between idiopathic bronchiectasis versus known cause of bronchiectasis. Bilateral upper lobe distribution is commonly seen in patients with cystic fibrosis and allergic bronchopulmonary aspergillosis, unilateral upper lobe distribution is commonest in patients with tuberculosis, and a lower lobe distribution is most often seen in patients after childhood viral infections. However, CT remains of little value in diagnosing specific aetiologies of bronchiectasis.

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