The current standard of CT technology is a multi-slice (usually 64 detector row) CT system, able to acquire submillimetre collimation images through the thorax in a short breath-hold. The decision to include abdominal, pelvic and intracranial assessment varies from centre to centre. However, a comprehensive brain, chest, abdomen and pelvis acquisition can be undertaken in very short order and the main rate-limiting steps are now patient identification, preparation and documentation rather than the acquisition of the data sets. Most institutions will routinely use intravenous contrast, although this is not mandatory. Not infrequently, difficulty with venous access, asthma, allergy or previous contrast reaction and impaired renal function will prevent contrast administration. A standard thoracic CT will be undertaken with the patient in supine position and the arms elevated. Imaging planning and dose reduction optimisation require an AP, and sometimes a lateral scout projection. If contrast medium is administered, then image acquisition is timed to optimise opacification of central pulmonary vasculature (usually 20–30 s). If an abdominal and pelvic study is also undertaken, this component is best acquired during the portal venous phase of contrast enhancement (65 s). This will require two short breath-holds and two preplanned acquisition ranges with some overlap at the lung bases.
The ability to produce isotropic voxels allows multiplanar reformatting to be undertaken as a routine, either by the radiographic staff or at the time of reporting by the radiologist.
The PET/CT technique is similar for the CT acquisition of the study, usually obtained from skull base to upper thigh. If the patient is also undergoing a conventional CT, the CT acquisition for PET co-registration can be of a low-dose non-contrast variety. Since the PET component of the acquisition takes considerably longer than the CT acquisition, in this situation the non-contrast low-dose CT will usually be undertaken during gentle respiration, to allow optimum co-registration with the PET data. Usually the PET acquisition takes between 5 and 7 bed couch positions, with each position taking up to 5 min, and therefore the whole study may take up to 35 min to acquire. More modern systems achieve the entire study in considerably less time.
MRI of the thorax is usually undertaken to answer a particular question as a problem-solving tool. In the context of lung cancer staging, the MR study is often to assess superior sulcus tumours, chest wall or thoracic invasion or to assess the integrity of the diaphragm.
Usually triplanar examinations are untaken with respiratory gating and T1 and T2 weighting. A variety of more refined techniques, including dynamic contrast-enhanced MR sequences for evaluation of lung nodules, have been described. Furthermore, dynamic ultrafast acquisitions can be utilised to assess fixation of a peripheral tumour to chest wall or mediastinal structures.
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