Low-dose CT: technique, reading methods and image interpretation

Abstract

The National Lung Cancer Screening Trial has recently demonstrated that screening of high-risk populations with the use of low-dose computed tomography (LDCT) reduces lung cancer mortality. Based on this encouraging result, the National Comprehensive Cancer Network guidelines recommended LDCT for selected patients at high risk of lung cancer. This suggests that an increasing number of CT screening examinations will be performed. The LDCT technique is relatively simple but some CT parameters are important and should be accurately defined in order to achieve good diagnostic quality and minimize the delivered dose. In addition, LDCT examinations are not as easy to read as they may initially appear; different approaches and tools are available for nodule detection and measurement. Moreover, the management of positive results can be a complex process and can differ significantly from routine clinical practice. Therefore this paper deals with the LDCT technique, reading methods and interpretation in lung cancer screening, particularly for those radiologists who have little experience of the technique.

Figure 1

(a) Transverse unenhanced low-dose CT scan of a 63-year-old man shows a non-solid nodule in the upper left lobe (arrow). (b) Transverse unenhanced low-dose CT scan of a 66-year-old woman shows a part-solid nodule in the lower left lobe (arrow). (c) Transverse unenhanced low-dose CT scan of a 58-year-old man shows a solid nodule in the upper right lobe (arrow). All 3 nodules were surgically removed and were found to be adenocarcinoma of the lung.

Figure 2

Transverse unenhanced low-dose CT scans show a slow-growing pulmonary nodule of the lower right lobe in a 61-year-old man. In 2012, the nodule was surgically removed and was found to be adenocarcinoma of the lung. The nodule measured 5.5 mm in 2007 (a), 8.5 mm in 2009 (b) and 11 mm in 2012 (c).