Use Conventional CT

In practice helical scanning for thorax has now become routine for CT imaging and in the main is used for diagnostic purposes,. There are a few instances where conventional CT may still be preferred and these are listed below :

• High resolution (HR) CT for detailed imaging of lung parenchyma . differentiation of pulmonary nodules and focal lung diseases. Incremental acquisition using narrow beam collimation , in the writers experience, is still protocol of choice. Nevertheless ,s studies are beginning to show that helical acquisition may provide similar information since a volume acquisition may provide similar information , since volume acquisition allow data be reconstructed retrospectively (Figure), to overlap slices directly through the centre of pulmonary nodules of areas of interest. This provides more information without further scanning of the patient and reduces partial volume artefact : however the detail may not be equal to that of incremental scanning
• Biopsy, aspiration, drainage, although helical acquisitions is useful for identification of lesion or collection, it has little advantage over conventional scanning for accurate localization. It has preciously been suggested that interpolation algorithms employed for image reconstruction, may produce a less than accurate representation . In practice, however , it seem to make little difference.
• Radiotherapy planning. Helical CT is not widely used as yet because patient translation along z –axis and image interpolation may affect treatment planning. 3d reformatting tough, can be used to aid planning

If helical acquisition is not an opinion then conventional slice by slice scanning using contiguous slices clustered together, if possible, to reduce the number of breath-hold, will provide information similar to that of helical scanning