The difference between the arterial phase and the venous phase is that one is the period when the arterial vessels are visualized and the other is the period when the venous vessels are visualized during a CT or MRI enhanced scan.
During CT or MRI enhancement scanning, the contrast agent is often injected from the vein in front of the elbow, and at the same time CT or MRI scanning is performed, the contrast agent flows rapidly within the blood vessels and enters the arteries and veins of the tissues and organs successively with the blood circulation. The period of time when the image is scanned after the contrast agent enters the arteries is called the arterial phase, and the period of time when the image is scanned after the contrast agent enters the veins is called the venous phase.
Enhancement scans can detect lesions that are overlooked on plain scanning (CT or MRI without contrast injection) and can identify lesions that are difficult to identify on plain scanning.
For example, if a low-density lesion is found after CT scanning of the liver, and it is not known whether the lesion belongs to a benign hemangioma or a malignant hepatocellular carcinoma, it is possible to further improve the enhanced CT examination, and then, according to the different image manifestations of the arterial and venous phases, it can be presumed that the lesion belongs to a kind of tumor, so as to guide the doctor’s next step in diagnosis and treatment.