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

From the Guidelines

Contrast-enhanced CT is the most suitable radiological assessment for hepatovascular imaging on CT abdomen, as it can demonstrate parenchymal heterogeneity and enhancement of lattice-like macroscopic bands of fibrosis throughout the hepatic parenchyma 1. For optimal hepatovascular imaging, a multiphasic CT protocol is recommended, consisting of non-contrast, arterial, portal venous, and delayed phases.

• The standard contrast agent is an iodinated contrast medium, typically administered at a rate of 3-5 mL/second.
• This protocol allows visualization of different vascular structures at their peak enhancement: hepatic arteries in the arterial phase, portal veins and hepatic parenchyma in the portal venous phase, and hepatic veins in the delayed phase.
• The multiphasic approach is essential because many hepatic lesions have characteristic enhancement patterns that aid in diagnosis, as noted in the evaluation for TIPS placement 1.
• Patients should be well-hydrated before the procedure and those with renal impairment may require alternative imaging or prophylactic measures to prevent contrast-induced nephropathy.
• Abdominal CT scan with contrast injection is preferred due to its accessibility and spatial resolution, which allows a comprehensive view of hepatic vein anatomy and detection of potential contraindications for TIPS placement 1.

From the FDA Drug Label

Contrast enhancement appears to be greatest immediately after bolus administration (15 seconds to 120 seconds). Thus, greatest enhancement may be detected by a series of consecutive two-to-three second scans performed within 30 to 90 seconds after injection (ie, dynamic computed tomographic imaging) A vascularized lesion is characterized by an increase in CT number in the few minutes after a bolus of intravascular contrast agent; it may be malignant, benign, or normal tissue, but would probably not be a cyst, hematoma, or other nonvascular lesion

The use of iohexol (IV) as a contrast agent can help to distinguish between vascularized and non-vascularized lesions in the abdomen, including hepatic vascular lesions, by enhancing computed tomographic imaging.

• The greatest enhancement can be detected immediately after bolus administration.
• Dynamic computed tomographic imaging can improve enhancement and diagnostic assessment of lesions.
• A vascularized lesion can be characterized by an increase in CT number after a bolus of intravascular contrast agent 2.

From the Research

Contrast Agents in Hepato Vascular Imaging on CT Abdomen

• The choice of contrast agent for CT abdomen imaging can significantly impact the quality of hepato vascular imaging 3, 4, 5.
• Studies have compared the effectiveness of different contrast agents, including iodinated and non-ionic agents, in enhancing hepatic and vascular structures 6, 5.
• The use of gadolinium contrast has been shown to be effective in reducing the incidence of contrast nephropathy in patients with chronic kidney disease 7.
• Optimal dosing of contrast material is crucial, with studies suggesting that a dose of 2.0-2.5 mL/kg of intravenous contrast material produces better results than 1.5 mL/kg or a fixed dose 3.
• Delay time also plays a significant role, with a 60-sec delay providing greater hepatic enhancement than a 45-sec delay for most contrast media 4.

Comparison of Contrast Agents

• Iohexol and iopamidol are second-generation non-ionic contrast media that offer improvements over conventional ionic contrast media 6.
• Iohexol 300, ioversol 240, and ioversol 320 have been compared in terms of hepatic enhancement and vascular attenuation, with varying results 4.
• Ionic contrast agents, such as iothalamate-60, have been shown to provide superior enhancement on delayed CT scans compared to non-ionic agents like iohexol-300 5.

Key Findings

• The type of contrast agent used can affect the degree of hepatic enhancement and vascular attenuation 4, 5.
• Gadolinium contrast is a potential alternative to iodinated contrast for patients with chronic kidney disease, reducing the risk of contrast nephropathy 7.
• Optimal dosing and delay time are critical in achieving high-quality hepato vascular imaging on CT abdomen 3, 4.