What is the role of contrast in evaluating hepatic vascular structures on Computed Tomography Angiography (CTA) of the abdomen?

From the Guidelines

Contrast-enhanced CT is the most suitable radiological assessment for evaluating hepatovascular structures on a CTA abdomen, as it provides a comprehensive view of hepatic vein anatomy and detects potential anatomical variations and contraindications 1.

Key Points

• The use of contrast material in CTA abdomen examinations is crucial for visualizing hepatovascular structures, including hepatic arteries, portal veins, and hepatic veins.
• Contrast-enhanced CT can demonstrate parenchymal heterogeneity and enhancement of lattice-like macroscopic bands of fibrosis throughout the hepatic parenchyma, making it more useful than noncontrast CT for assessing hepatic fibrosis and cirrhosis 1.
• Factors that can affect contrast enhancement include timing of image acquisition, rate of contrast injection, patient factors such as cardiac output, and technical parameters of the CT scanner.
• Radiologists look for uniform enhancement of vessels without filling defects, which could indicate pathology such as thrombosis, stenosis, or vascular malformations.
• The most recent and highest quality study recommends the use of contrast-enhanced CT for pre-TIPS evaluation, taking into account its accessibility and spatial resolution 1.

Recommendations

• Use contrast-enhanced CT for evaluating hepatovascular structures on a CTA abdomen.
• Consider the timing of image acquisition, rate of contrast injection, and patient factors when interpreting contrast enhancement.
• Look for uniform enhancement of vessels without filling defects to rule out significant vascular abnormalities.
• Use the most recent and highest quality study as a reference for clinical decision-making, in this case, the 2024 study by the French guidelines on TIPS 1.

From the Research

Hepato Vascular Contrast on CTA Abdomen

• The use of contrast material for spiral CT of the abdomen has been studied to determine the relative effects of delay time, contrast agent concentration, and contrast agent volume on hepatic enhancement and on aortic and portal vein attenuation 2.
• A study found that a 60-sec delay provided greater hepatic enhancement than did a 45-sec delay for three different contrast media, and the portal vein attenuation achieved after contrast medium administration was significantly greater with a 60-sec delay than with a 45-sec delay for all three contrast media 2.
• Another study defined normal values of the beginning and duration of the hepatic arterial phase (HAP) during contrast-enhanced computed tomography (CT) and found that the mean lag time of the HAP was 5.4 seconds after the aorta and the mean duration was 8.6 seconds 3.

Contrast Agents for Vascular Imaging

• A comparison between iohexol 350 mg I/ml and iopamidol 370 mg I/ml found no difference between the contrast media with regard to increase in contrast enhancement in the liver, vena cava, aorta, and spleen 4.
• A study compared iodixanol and iohexol for vascular imaging on computed tomography and found that the vascular attenuation provided by a 9.3% lower iodine concentration of iso-osmolar iodixanol is equal to that given by hyperosmolar iohexol 5.
• Non-contrast CT scans can still provide clues to vascular disorders, and alternative imaging options can be discussed 6.

Key Findings

• Delay time, contrast agent concentration, and contrast agent volume can affect hepatic enhancement and vascular attenuation 2.
• The hepatic arterial phase has a short duration, making it challenging to image the entire liver during this phase without multidetector CT scanners 3.
• Different contrast agents can have similar effects on contrast enhancement, and the choice of contrast agent may depend on individual patient factors 4, 5.