Contrast extravasation on the arterial phase that grows and changes shape on the portal venous phase localises the bleed; the CTA map sends the catheter to the right artery.
Orient first
- CTA detects bleeding of about 0.3–0.5 mL/min; catheter angiography needs a higher rate.
- The non-contrast phase separates hyperdense material in the bowel (pills, prior contrast) from extravasation.
- Lower GI bleeds need superselective embolisation to avoid bowel ischaemia.
Acquire the study
- Triphasic CT: non-contrast, arterial and portal venous phases; no oral contrast.
The manoeuvre
- Non-contrast series: hyperdense intraluminal material already present (not extravasation).
- Arterial phase: contrast blush in the lumen; which bowel segment.
- Portal venous phase: pooling that grows and changes shape.
- Map the supplying artery (SMA, IMA, gastroduodenal, left gastric) and cause (diverticulum, tumour, angiodysplasia, ulcer).
What confirms it
- Contrast extravasation that grows between phases in a bowel segment.
What licenses you to exclude it
- A negative CTA does not exclude intermittent bleeding; it excludes active bleeding above the detection threshold at that time.
The classic misread
- Calling hyperdense pills or prior barium extravasation without the non-contrast phase.
- Giving oral contrast before CTA.