Effect of PaCO2 on the vessel delineation in brain MR angiography

MR angiography (MRA) is non-invasive modality that can provide information about vascular structures as well as flow-related characteristics. We evaluated whether or not MRA can depict alteration of cerebral hemodynamics by changing arterial PaCO2. We performed three-dimensional cerebral MRA based on time-of-flight method in six normal volunteers on a 0.5 T unit. During the study in each patient, we measured arterial PaCO2 under spontaneous hyperventilation, normal breathing, and inhalation of 7% CO2, respectively. MR angiograms obtained under above conditions were visually inspected with measurement of signal intensities of middle cerebral arteries (MCAs) on the maximum-intensity-projection images and the results were compared with blood-sampled PaCO2 values. There was marked improvement of the delineation of major cerebral vessels as increasing PaCO2, indicating significant correlation between PaCO2 and MCA signal intensities (r=0.54, p<0.01). We conclude that combination of PaCO2 change and MRA is useful to detect hemodynamic information about the cerebral circulation. (author)