Name the typical phases of contrast enhancement in CT imaging and what each phase highlights?

• A. Non-contrast; arterial phase; venous phase; delayed/excretory phase; but the venous phase does not enhance parenchyma.
• B. Non-contrast; arterial phase; venous phase; lymphatic phase.
• C. Non-contrast; arterial phase; venous phase; lymphatic phase.
• D. Non-contrast; arterial phase; venous phase; delayed/excretory phase.

Answer: (D)

The question tests understanding of the usual CT contrast-enhancement timeline and what each phase reveals. After injecting iodinated contrast, CT scans are typically acquired in a sequence that starts with no contrast, then captures arterial inflow, then venous outflow, and finally a delayed/excretory phase as the contrast is cleared by the kidneys.

Non-contrast imaging provides baseline densities, helping identify calcifications, hemorrhage, or stones. The arterial phase highlights arteries and hypervascular lesions, making it best for evaluating arterial anatomy and tumors that feed on arterial blood. The venous phase emphasizes parenchymal enhancement and the venous circulation; for many organs, this phase shows the characteristic parenchymal enhancement pattern and is essential for assessing overall organ perfusion and vascular structures. The delayed or excretory phase occurs several minutes after injection as the contrast is excreted by the kidneys, highlighting the urinary collecting system, ureters, and bladder, and it can reveal lesions with delayed washout or collecting system abnormalities.

One option mentions a lymphatic phase, which isn’t a standard CT enhancement phase, and another incorrectly claims the venous phase doesn’t enhance parenchyma, which isn’t true. The standard sequence is non-contrast, arterial, venous, delayed/excretory.