CT Chest — Unenhanced

Lung apices to below the costophrenic angles.

Typical, not policy

Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.

When to use it

Nodule detection, characterisation and follow-up under a structured surveillance schedule.
Suspected infection or its complications where the parenchyma, not the mediastinum, is the question.
Follow-up of known parenchymal disease where a previous unenhanced study is the comparator.
Any chest question in a patient in whom iodinated contrast is contraindicated and the parenchymal answer suffices.

Technique

Nodule follow-up should replicate the prior technique — same inspiratory effort, comparable slice thickness and reconstruction — because apparent growth is otherwise a technique artefact.
Volumetric measurement, where used, requires thin sections and a consistent reconstruction kernel across timepoints.

Where it goes wrong

Comparing a thin-section volumetric study against an old thick-section one manufactures growth or stability that is not there.
Using an unenhanced study to exclude nodal disease or mediastinal invasion under-calls both.
Shallow inspiration produces dependent atelectasis that is repeatedly mistaken for a basal nodule or infiltrate.

Clinical questions that reach this study

Suspected pancreatic mass or painless obstructive jaundice Suspected cholangiocarcinoma Colorectal cancer — staging Incidental pulmonary nodule — characterisation and follow-up Known or suspected lung cancer — staging Suspected pneumonia and non-resolving consolidation Suspected empyema or complicated parapneumonic effusion Undiagnosed unilateral pleural effusion Suspected interstitial lung disease Suspected bronchiectasis Haemoptysis Suspected pneumothorax Suspected superior vena cava obstruction Staging or completion CT in a known solid tumour Liver assessment in a hypervascular primary Response assessment on systemic therapy Suspected or newly diagnosed lymphoma Metastatic disease with no identified primary Head and neck cancer — staging and post-treatment surveillance Indeterminate renal mass or suspected renal cell carcinoma Suspected phaeochromocytoma or paraganglioma Bladder cancer — pretreatment staging Acute scrotum and scrotal mass Suspected ovarian cancer or indeterminate adnexal mass

Contrast

None

Acquisition

Breathing: Single full inspiratory breath-hold.
Reconstruction: Thin axial reconstructions in soft-tissue and lung kernels with multiplanar reformats.
Preparation: Full inspiratory breath-hold, practised before the acquisition. Arms above the head; arms down doubles streak artefact through the upper thorax.

Phases

Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.

Non-contrast (unenhanced)No injection. Acquired before any contrast is given.
Shows intrinsic tissue attenuation, and nothing else. The transferable principle is that contrast is anti-signal for anything that is already dense: calcification, acute haemorrhage, urinary and biliary calculi, iodine-containing or haemorrhagic fluid, and intrinsic fat all lose conspicuity, or become uninterpretable, once surrounding tissue enhances. It is also the only baseline against which enhancement can be measured, so any protocol that quantifies enhancement or washout (a lesion "enhances by X HU", adrenal absolute washout, renal mass characterisation) is arithmetically impossible without it. Conversely, an unenhanced series adds dose and no information whenever the question is purely about vascularity or perfusion.

Safety checks this protocol carries

Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.

Child-sized technique and contrast dose· radiographer at scan
Pregnancy status before an ionising exposure· radiographer at scan

References

Fleischner Society: interstitial lung abnormalities detected incidentally on CT — position paper.