INFLUENCE OF ARTERIAL PARTIAL-PRESSURE OF CARBON-DIOXIDE ON CEREBRAL MRA IN NORMAL VOLUNTEERS

Objective: Signal intensity of MR angiography (MRA) is influenced by the physiological factors of flowing blood in the vessels. We examined whether MRA can detect a cerebral hemodynamic change induced by reducing or elevating the arterial partial pressure of carbon dioxide (P(a)co(2)). Materials and Methods: Cerebral MRA was performed in six normal volunteers, each having three measurements during hyperventilation, normal breathing, and 7% CO2 inhalation. The MRA data were obtained by a 0.5 T wholebody scanner and a time-of-flight technique of three-dimensional GE imaging. In addition to the visual inspection, the signal intensity and the lengths of the middle cerebral artery (MCA) and posterior cerebral artery (PCA) were estimated in relation to P(a)co(2). Results: The MRA appearances of major cerebral arteries were remarkably different depending on the breathing conditions. There was significant difference in the mean signal intensity (p < 0.01) and the mean length (p < 0.01) of the MCA and PCA between the hyperventilation and normal breathing trials. Conclusion: The MRA signal was sensitive to the changes in P(a)co(2) level of flowing blood. This phenomenon may result from changes in the velocity of blood flow in major cerebral arteries.