CT Pancreas — Dual Phase with Water Distension
Pancreas and upper abdomen for the pancreatic phase; whole abdomen and pelvis for the portal venous phase when staging.
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 or known pancreatic ductal adenocarcinoma, for detection and for resectability staging.
- Characterisation of a cystic pancreatic lesion.
- Localisation of a suspected functioning neuroendocrine tumour, which is typically hypervascular in the pancreatic phase.
- Assessment of complications of pancreatitis, including collections, necrosis and vascular complications.
Technique
- The pancreatic parenchymal phase — commonly quoted at around 40-45 s after the start of injection — is where tumour-to-parenchyma attenuation difference peaks, and where arterial vascular contact is assessed.
- The portal venous phase at around 70 s is where liver metastases and venous involvement are best seen. Sources quote these two delays fairly consistently at approximately 40 s and 70 s.
- A high injection rate matters: the parenchymal-phase contrast difference depends on iodine delivery rate.
- Water distension of the stomach and duodenum shows the duodenal wall and the ampullary region, which positive contrast conceals.
Where it goes wrong
- A single portal venous acquisition under-detects small isoattenuating pancreatic tumours and under-stages arterial involvement.
- Positive oral contrast obliterates the duodenal interface and creates streak across the pancreatic head.
- Timing the "arterial" phase too early gives an angiographic phase in which the parenchyma has not yet enhanced and the tumour-to-parenchyma difference has not developed.
- Thick reconstructions defeat curved reformats along the duct and the vascular contact assessment that determines resectability.
Contrast
Water (commonly 500-750 mL) as the neutral luminal agent shortly before scanning, plus typically 100-150 mL of non-ionic iodinated contrast at 3-5 mL/s.
- No positive oral contrast — it obscures the duodenal wall and streaks the peripancreatic vessels.
Acquisition
- Breathing
- Matched breath-hold for both phases.
- Reconstruction
- Thin axial reconstructions with curved and multiplanar reformats along the pancreatic duct and along the coeliac axis, superior mesenteric artery and vein, plus maximum-intensity projections for vascular contact assessment.
- Preparation
- Water as neutral luminal contrast shortly before scanning; positive oral contrast defeats the purpose by obscuring the duodenal interface and the peripancreatic vessels. Power-injectable cannula for an injection rate typically in the 3-5 mL/s range.
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.
- Neutral oral contrast (enterography preparation)Large-volume ingestion over roughly the 45–60 min before scanning (typically of the order of 1.3–2 L in divided doses). Confirm locally.
A near-water-attenuation agent distends the lumen without hiding the wall. The transferable principle is that when the DISEASE IS IN THE WALL, the lumen must be made transparent rather than bright: a distended, low-attenuation lumen against enhancing mucosa is what makes mural hyperenhancement, wall thickening, stratification and comb-sign mesenteric hyperaemia measurable. Neutral agents are formulated to resist absorption so that distension survives to the terminal ileum. The cost is that they forfeit the one thing positive agents do best — an unenhanced-appearing lumen cannot demonstrate a leak — and that adequate distension depends on the patient completing an unpleasant volume on schedule, making this the phase most often defeated by preparation failure rather than by scanner technique.
- Pancreatic parenchymal phaseTypically ~40–50 s after the start of injection. Confirm locally.
Pancreatic parenchyma reaches peak enhancement slightly later than the arteries but before the liver is portally loaded. The transferable principle is the inverse of the arterial one: when the TARGET is hypovascular, conspicuity is created by maximising the BACKGROUND, so the phase is timed to the gland rather than to the lesion. Peripancreatic arteries and veins are simultaneously well opacified, which is why the same acquisition doubles as the vascular-contact assessment that drives resectability. Scanning a hypovascular gland lesion in the portal venous phase alone systematically loses small tumours.
- 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