CT Extremity — Unenhanced, Thin Section
The joint or bony region in question with a margin above and below; the contralateral side is included only when a direct comparison is genuinely needed.
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
- Suspected fracture not shown or not adequately characterised on radiographs — scaphoid, radial head, tibial plateau, calcaneus, complex pelvic and acetabular injuries.
- Pre-operative planning and fracture classification, including articular step and comminution.
- Assessment of union or non-union and of hardware position and loosening.
- Characterisation of a bone lesion where matrix, cortical integrity or periosteal reaction is the question.
- Suspected osteoid osteoma, where the nidus is a CT diagnosis.
Technique
- Position the region of interest at the scanner isocentre; scanning both limbs together for convenience degrades the one you care about.
- Reformats aligned to the joint axis (rather than to the scanner axes) are what the surgeon plans from.
- Where metalwork is present, a higher tube potential combined with a metal-artefact reduction reconstruction, and thin sections with a moderately sharp kernel, materially improves the bone-implant interface. Tin-filtered high-kV and dual-energy approaches are further options where available.
Where it goes wrong
- Thick reconstructions blur non-displaced fractures, which is the exact question a negative radiograph has escalated.
- Scanning through metalwork with default parameters produces streak that hides periprosthetic lucency and fracture.
- A soft-tissue mass question is not answered by an unenhanced bone protocol; MRI or a contrast-enhanced study is the right test.
- Failing to include the joint above or below in a limb fracture leaves an associated injury undetected.
Clinical questions that reach this study
Contrast
Acquisition
- Reconstruction
- Sub-millimetre acquisition reconstructed in bone and soft-tissue kernels with multiplanar reformats aligned to the anatomy of interest and, where useful, 3D volume rendering with the overlying bones removed.
- Preparation
- Position the region of interest as close to the isocentre as possible and, where feasible, out of the contralateral limb — scanning both legs together doubles scatter across the joint you care about. Declare metalwork on the request so a metal-artefact protocol can be selected in advance.
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