# Routine CT Protocols > Routine CT protocols in Radiology Technology: arterial, portal venous and delayed phases, triple-phase liver, renal mass protocol, CTPA timing and CT urogram. - Canonical URL: https://prepelephant.com/topics/allied/radiology-and-imaging-technology/ct-protocols-routine - Exam / course: Allied Health · Subject: Radiology and Imaging Technology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Routine CT Protocols", PrepElephant, https://prepelephant.com/topics/allied/radiology-and-imaging-technology/ct-protocols-routine ## Direct answer A contrast CT protocol is defined above all by phase timing: late arterial phase around 30-40 seconds from injection, portal venous phase 60-70 seconds, and delayed (equilibrium or excretory) phases at 3-5 minutes and beyond. The liver mass protocol runs non-contrast, arterial and portal venous (with delayed imaging for washout and capsule); the renal mass protocol adds corticomedullary, nephrographic and excretory phases; CT pulmonary angiography fires at about 15-25 seconds or on bolus tracking in the pulmonary artery; CT urogram images the excretory phase at 5-10 minutes. Bolus tracking (a region of interest in the aorta triggering at roughly +100 HU) replaces fixed delays for vascular studies, and the technologist's timing accuracy decides whether the study answers the clinical question. ## What you must remember - Phase clock: late arterial 30-40 s, portal venous 60-70 s, equilibrium/nephrographic 90-120 s, delayed 3-5 min; excretory (urogram) 5-10 min. - Bolus tracking: a region of interest in the aorta (or pulmonary artery for CTPA) triggers the scan at a threshold near +100 HU — the standard answer for vascular timing. - Triple-phase liver: non-contrast, arterial, portal venous; hepatocellular carcinoma shows arterial hyperenhancement with portal/delayed washout — the pattern the protocol exists to capture. - Renal mass protocol: corticomedullary (~35 s) for vascular anatomy, nephrographic (~100 s) — the most sensitive phase for small renal masses — and excretory for the collecting system. - Pancreatic protocol: pancreatic phase 35-45 s plus portal venous, with water as oral contrast to distend the duodenum. - CTPA: bolus tracking in the pulmonary artery, saline chaser, breath-hold; filling defects confirm or exclude embolism — late timing misses emboli. - CT urogram: excretory-phase thin-section imaging of the whole urinary tract after contrast, for haematuria and urothelial tumours. - Non-contrast phase first for stone disease (nearly all stones are visible on CT) and as the baseline for enhancement measurement; stroke protocols begin with non-contrast brain CT to exclude haemorrhage before thrombolysis. - Oral contrast choices: water (neutral) for stomach and pancreatic studies; dilute iodinated positive contrast for bowel pathology; weight-based intravenous volume (commonly 1-1.5 mL/kg of 300-350 mgI/mL, 60-80 mL typical adult) with a 30-40 mL saline chaser. ## Timing a triple-phase liver study Walk a cirrhotic patient's protocol through the clock and every delay earns its place. The non-contrast phase maps baseline density — without it, later "enhancement" cannot be measured. The arterial phase at about 35 seconds — late arterial — is when hypervascular tumours glow: hepatocellular carcinomas steal arterial supply, and this phase alone catches them. The portal venous phase at 60-70 seconds is when normal liver parenchyma peaks via portal inflow; a tumour that blushed arterially now falls behind it — washout — a diagnostic signature impossible without both phases. Delayed imaging at 3-5 minutes captures capsule and the retention pattern of cholangiocarcinoma. Now the failure modes the technologist polices. A patient who breath-holds differently between phases misregisters small lesions from phase to phase — coach the same breath-hold every time. And the contrast argument: enhancement measurement needs identical injection rate and volume, so "half the dose, same timing" silently corrupts the washout logic. The protocol is not a button labelled "triple phase liver" but a coordinated physiological experiment — tube, pump, patient and clock — and the radiographer runs three of the four. ## Where students slip Phase numbers are memorised as isolated facts and then shuffled: 35 seconds belongs to late arterial and pancreatic phases, 70 to portal venous, 100 to nephrographic, 5 minutes to excretory — build the ladder, do not collect digits. Second, the nephrographic phase is forgotten as the most sensitive for small renal masses; students name corticomedullary for its drama. Third, stroke sequencing: the non-contrast brain CT comes first because haemorrhage excludes thrombolysis; a protocol that leads with CTPA has ordered the study around the wrong question. And oral contrast chosen by habit — dense positive contrast outlining bowel — ruins a pancreatic protocol where water distension of the duodenum is the entire point. ## Frequently asked questions ### What are the standard contrast phases and their timings? Late arterial about 30-40 seconds after injection, portal venous 60-70 seconds, equilibrium/nephrographic 90-120 seconds, and delayed or excretory phases from 3-5 minutes onward. ### How does bolus tracking individualise timing? A region of interest monitors enhancement in a vessel (aorta or pulmonary artery), triggering the scan when it reaches a set threshold (about +100 HU), correcting for each patient's circulation time. ### Why does a liver mass protocol need arterial and portal venous phases? Hepatocellular carcinoma enhances in the arterial phase and washes out relative to the portal-phase liver; capturing both patterns is the diagnostic basis of the study. ### Which phase is most sensitive for small renal masses? The nephrographic phase (about 100 seconds), when cortex and medulla enhance uniformly, exposing otherwise isodense small tumours. ### How is CT pulmonary angiography timed? By bolus tracking in the pulmonary artery or a fixed short delay of about 15-25 seconds with a rapid injection and saline chaser — late timing misses emboli as the bolus passes into systemic circulation.