CT Chest — Low Dose Lung Cancer Screening

Lung apices to the costophrenic angles, single inspiratory volumetric acquisition.

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

Baseline and annual incidence screening in an asymptomatic high-risk individual meeting an established eligibility rule.
Structured interval follow-up of a screen-detected nodule under a reporting and management system such as Lung-RADS.

Technique

Programme standards set an upper limit on dose rather than a fixed technique: a volume CT dose index of about 3 mGy or less for a standard-sized patient, adjusted up or down for habitus, is the widely cited benchmark, with an effective dose of roughly 1 mSv.
Contrast has no place in a screening acquisition.
Consistency between screening rounds matters more than absolute image quality: reconstruction kernel and slice thickness should not drift between timepoints.

Where it goes wrong

Applying screening dose parameters to a symptomatic diagnostic question produces images too noisy for the actual clinical problem.
Changing reconstruction kernel or slice thickness between rounds invalidates volumetric growth assessment.
A screening study is not a staging study: it will not characterise mediastinal nodes or pleural disease.
In a larger patient, holding the dose at the standard-size benchmark rather than scaling it up produces a non-diagnostic scan.

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 sections, ideally 1 mm or less, in a lung kernel suitable for volumetric nodule measurement, plus a soft-tissue series for incidental findings.
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