CT with IV contrast

A woman undergoing CT with IV contrast.

Author: Mikael Häggström
Contrast CT is CT scan using radiocontrast, and in Radlines it refers to a CT scan using IV contrast except otherwise noted.

Bolus tracking is where a specified location within the circulatory system is monitored during IV contrast infusion, and the timing of the main imaging is counted from when the contrast reaches this location (sufficiently to achieve a specified threshold).

Washout is where tissue loads radiocontrast during arterial phase, but then returns to a rather hypodense state in venous or later phases. This is a property of for example hepatocellular carcinoma as compared to the rest of the liver parenchyma.

Contents

Contrast-induced nephropathy

Risk factors

The Roxana Mehran score predictor applies the following ten variables:

• Age (4 points if older than 75 years old)
• Anemia (3 points)
• Use of an intra-aortic balloon pump (5 points)
• eGFR 60 to 40 (2 points)
• eGFR 40 to 20 (4 points)
• eGFR less than 20 (6 points)
• Hypotension (5 points, if systolic BP less than 80 mmHg for at least one hour requiring inotropic support)
• Contrast media volume (1 point per 100 ml)
• Congestive heart failure (5 points)
• Diabetes (3 points).

A risk score of less than 6 carries a risk of 7.5% to score more than 16 carries up to 57% risk.

Alternatives

Iodine concentration	Maximum volume
240 mg/ml	4.2 ml *GFRml/min
350 mg/ml	2.9 ml *GFRml/min In people with risk factors, the main alternatives are: Adjustment of the contrast dose. Evidence suggests that contrast doses should be limited to a ratio of grams of iodine to glomerular filtration rate (Igram / GFRml/min) of a maximum of 1. The local practice at NU Hospital Group has a Igram/GFR ratio of maximum 0.7 in patients with GFR ≥45 ml/min. It recommends a ratio of maximum 0.5 if GFR is lower, or in the presence of risk factors. Using no intravenous contrast' for the investigation. Switching to another modality such as ultrasonography or MRI Treating or mitigating risk factors. Hydration by drinking or intravenous volume expander, either before or after contract administration, decreases the risk of contrast-induced nephropathy. Phases Depending on the purpose of the investigation, there are standardized protocols for time intervals between intravenous radiocontrast administration and image acquisition, in order to visualize the dynamics of contrast enhancements in different organs and tissues. The main phases thereof are as follows: Phase Time from injection Time from bolus tracking in proximal aorta Targeted structures and findings Non-enhanced CT (NECT) - - Calfications Fat in tumors such as in adrenocortical adenomas Fat-stranding as seen in inflammation such as appendicitis, diverticulitis and omental infarction Pulmonary arterial phase 6-13 sec - Pulmonary embolism Pulmonary venous phase 17-24 sec - Early systemic arterial phase 15-20 sec immediately Arteries, without enhancement of organs and other soft tissues. Late systemicarterial phase Sometimes also called "arterial phase" or "early venous portal phase" 35-40 sec 15-20 sec All structures that get their blood supply from the arteries have optimal enhancement. Some enhancement of the portal vein Pancreatic phase 30 or 40 - 50 sec 20-30 sec Pancreatic cancers become hypodense compared to the parenchyma. Hepatic (most accurate) or late portal phase 70-80 sec 50-60 sec Liver parenchyma enhances through portal vein supply, normally with some enhancement of the hepatic veins. Nephrogenic phase 100 sec 80 sec All of the renal parenchyma enhances, including the medulla, allowing detection of small renal cell carcinomas Systemic venous phase 180 sec 160 sec Detect venous thrombosis Delayed phase Sometimes called "wash out phase" or "equilibrium phase" 6-15 minutes 6-15 minutes Disappearance of contrast in all abdominal structures except for tissue with fibrosis, which appears more radiodense. Gastrointestinal contrast Rectally administered contrast is indicated in cases where a suspicion remains of penetrating trauma to the colon where an initial CT shows no reason for immediate surgery. References