CT Lumbar Spine — Unenhanced, Thin Section
T12 through the sacrum and sacroiliac joints, extended when a specific level or hardware is in question.
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 lumbar fracture after trauma, or an insufficiency fracture where radiographs are equivocal.
- Suspected pars defect or spondylolysis, particularly in a young athlete.
- Assessment of instrumentation, fusion mass and screw position after surgery.
- Bony detail in known spinal malignancy or infection, complementing rather than replacing MRI.
- Degenerative or radicular symptoms only when MRI is contraindicated or unavailable.
Technique
- Oblique sagittal reformats through the pars are the productive plane for spondylolysis.
- Where metalwork is present, a higher tube potential together with a metal-artefact reduction reconstruction materially improves assessment of the bone-implant interface.
Where it goes wrong
- CT is a poor substitute for MRI in cauda equina syndrome, disc herniation and cord or nerve root compression; substituting it because it is quicker answers a different question.
- A study in an unstable patient acquired without reformats effectively wastes the exposure.
- Streak from bilateral hip prostheses degrades the lower lumbar levels; anticipate it and adjust technique before scanning.
Clinical questions that reach this study
Contrast
Acquisition
- Reconstruction
- Thin-section bone and soft-tissue reconstructions with sagittal and coronal reformats; oblique reformats along the pars interarticularis where spondylolysis is the question.
- Preparation
- No preparation.
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