Which structure indicates the beginning of the venous phase of a cerebral blood flow study?

The beginning of the venous phase in a cerebral blood flow study is indicated by the superior sagittal sinus. In nuclear medicine, particularly during studies that assess cerebral perfusion, the phases of blood flow are significant. The arterial phase, which follows the injection of the radiotracer, showcases the passage of blood through the arterial system that supplies the brain. As the blood enters the veins, the superior sagittal sinus – a major venous structure located at the top of the brain – becomes prominent.

During the venous phase, the contrast or radiotracer can be seen pooling in the superior sagittal sinus as it collects blood from the brain. This transition from the arterial supply to the venous drainage is critical for understanding the dynamics of cerebral circulation. Other structures such as the anterior cerebral arteries and carotid arteries are part of the arterial phase, while the nasopharynx does not play a role in the assessment of cerebral venous drainage. Therefore, identifying the superior sagittal sinus accurately marks the delineation between these two phases of cerebral blood flow.