CT Abdomen and Pelvis — Unenhanced

Diaphragm to the pubic symphysis.

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

Iodinated contrast genuinely contraindicated and the clinical question is one unenhanced CT can still answer.
Suspected retroperitoneal or intraperitoneal haemorrhage where acute blood density is the finding.
Suspected bowel obstruction or perforation where free gas and calibre change carry the diagnosis.
Assessment of calcification, stones or radio-opaque foreign material.
Baseline series before a targeted multiphase protocol.

Technique

Where contrast is being withheld on renal grounds, record why: the vetting decision and the fallback should travel together.
The diagnostic cost of dropping contrast varies enormously by indication — it is modest for obstruction and near-total for solid organ lesion characterisation.

Where it goes wrong

Unenhanced CT cannot reliably exclude bowel ischaemia, abscess or solid organ injury; substituting it silently changes what the report can say.
Low-attenuation collections and unopacified bowel loops are easily confused without luminal or vascular contrast.
An unenhanced study reported as "no acute abnormality" can be read by the referrer as a negative full study — the limitation belongs in the report, and the vetting note should anticipate it.

Clinical questions that reach this study

Suspected intra-abdominal abscess or collection Suspected appendicitis Suspected malrotation with midgut volvulus Major trauma — whole-body (pan-scan) versus selective CT Suspected acute diverticulitis Suspected bowel obstruction Suspected gastrointestinal perforation Suspected acute mesenteric ischaemia Acute pancreatitis — severity and complication assessment Suspected acute cholecystitis Obstructive jaundice and suspected biliary obstruction Suspected cholangiocarcinoma Colorectal cancer — staging Rectal cancer — local staging and restaging Crohn disease — small bowel assessment and monitoring Suspected perianal fistula or perianal sepsis Acute colitis Suspected deep vein thrombosis Acute pelvic pain in the reproductive age group (including suspected PID and tubo-ovarian abscess)Adnexal mass — characterisation and risk stratification Staging or completion CT in a known solid tumour Response assessment on systemic therapy Suspected or newly diagnosed lymphoma Metastatic disease with no identified primary

Contrast

None

Acquisition

Breathing: Single breath-hold.
Reconstruction: Thin axial reconstructions with coronal and sagittal reformats and a bone series.
Preparation: Fasting for a few hours is common practice where IV contrast is planned, though it is not a safety requirement for iodinated contrast. Oral contrast, if any, is a protocol decision and should not be given by default.

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

AAPM adult routine abdomen/pelvis CT protocols.