CT Abdomen and Pelvis — Trauma

Diaphragm to the lesser trochanters, including the whole bony pelvis.

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

Blunt or penetrating abdominal trauma in a haemodynamically stable or stabilised patient.
Suspected solid organ injury, active haemorrhage or mesenteric injury.
Suspected pelvic fracture with vascular injury.

Technique

The arterial acquisition identifies active arterial extravasation and pseudoaneurysm; the portal venous acquisition grades parenchymal injury. A split-bolus single-pass technique achieves much of both at roughly half the dose and is standard practice in several major trauma centres.
DUAL-PHASE timing, stated explicitly: the arterial acquisition is bolus-tracked in the abdominal aorta at roughly 100-150 HU above baseline with a post-trigger diagnostic delay of about 5-10 s, or run at a fixed delay of about 25-30 s from the start of injection where tracking is not used; the portal venous acquisition then follows at roughly 60-80 s from the start of the same injection.
SPLIT-BOLUS timing, stated explicitly: the injection is divided and the two portions are separated so that a SINGLE acquisition catches the first portion in the venous phase and the second in the arterial. Published regimens differ — a common approach gives roughly a third to a half of the volume, pauses about 25-35 s, gives the remainder, and acquires once at roughly 25-35 s after the second injection (about 60-70 s after the first). Other published regimens use a much shorter inter-injection interval of around 10 s with a correspondingly later single pass. The interval and the acquisition delay are a matched pair and cannot be changed independently.
A delayed acquisition through the kidneys and bladder is added when urinary tract injury is suspected — haematuria, a renal injury on the earlier phases, or pelvic fracture with bladder concern. The excretory delay is longer than a routine delayed phase: roughly 5-10 minutes from injection is needed to opacify the collecting systems and ureters enough to call a leak.
Which of the two techniques a department runs is a departmental decision, not a per-patient one, and the numbers above are typical rather than settled — split-bolus regimens in particular vary considerably between published series and between scanner generations. Confirm locally.
Oral contrast has no role: it delays the study and does not improve detection of bowel injury.

Where it goes wrong

A portal-venous-only study can miss active arterial bleeding and under-stages vascular injury.
Split-bolus images look different from conventional phases — reading them as if they were a standard portal venous study leads to misinterpretation of enhancement, and consistency of protocol across a department matters more than the choice itself.
Omitting the delayed series in suspected renal or bladder injury leaves collecting system or bladder rupture undiagnosed.
Arms down through the torso drives streak across the upper abdomen; where injuries permit, arms should be up.

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

Iodinated, intravenous

Typically 100-150 mL of non-ionic iodinated contrast at 3-4 mL/s, either as two separate acquisitions or as a split bolus designed to give arterial and parenchymal enhancement in a single pass.

No oral contrast.

Acquisition

Breathing: Breath-hold where the patient can comply; quiet respiration otherwise.
Reconstruction: Thin axial reconstructions with multiplanar soft-tissue and bone reformats; the spine and pelvis are reformatted from this dataset rather than rescanned.
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.

CT angiography, bolus-trackedNo fixed delay. A monitoring ROI is placed in the target vessel (commonly the aorta) and acquisition triggers at a set attenuation rise — a ~100 HU threshold is widely used — followed by a short diagnostic delay of a few seconds for table movement and breath-hold instruction. Confirm locally.
This is not a separate physiological phase so much as a technique for hitting one reliably. The transferable principle is that a fixed delay assumes an average circulation, and the patients who most need vascular imaging — the shocked, the failing, the arrhythmic, the aneurysmal — are precisely those whose circulation time is furthest from average. Tracking the bolus in the target vessel replaces that assumption with a measurement, so peak arterial opacification is achieved in the individual patient. The trade-off is that the technique commits the scan to whatever the monitoring ROI sees: a badly placed ROI, a mistimed breath-hold or a threshold reached by a contralateral vein produces a systematically mistimed study rather than a slightly degraded one.
Portal venous phaseTypically ~60–90 s after the start of injection. Confirm locally.
The portal vein and hepatic veins are opacified and the liver is at maximum parenchymal enhancement; bowel wall, mesentery, spleen and peritoneum are all well enhanced. The transferable principle is that HYPOVASCULAR lesions are most conspicuous when the BACKGROUND peaks, so this is the single most productive general-purpose abdominal phase and the correct default when the question is "what is wrong in this abdomen?". Its corollary is the classic error: a hypervascular lesion that was obvious 30 s earlier can become isodense and invisible here, so a normal portal venous study never excludes hypervascular disease.

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.

Prior contrast reaction and elective premedication· nurse pre scan
Intravenous access adequate for the planned injection· radiographer at scan
Metformin and iodinated contrast· radiographer at scan
Child-sized technique and contrast dose· radiographer at scan
Pregnancy status before an ionising exposure· radiographer at scan
Kidney function and intravenous iodinated contrast· radiographer at scan

References

Triple-contrast versus intravenous-contrast-only CT for penetrating torso trauma — comparative series report similar accuracy, and practice differs by centre.
Beenen LFM, et al. Split-bolus technique in polytrauma: a prospective study on scan protocols. Acta Radiol 2015.
Diagnostic value of the split-bolus CT protocol in blunt abdominal trauma compared with standard portal venous phase imaging.
ACR Appropriateness Criteria — Renal Trauma: an excretory-phase acquisition, conventionally at around 5-10 minutes, is required to demonstrate collecting system or ureteric injury.