Neoangiogenesis in association with moyamoya syndrome shown by estimation of relative recirculation based on dynamic contrast-enhanced MR images.

BACKGROUND AND PURPOSE This study examined abnormalities of the recirculation phase of the contrast medium concentration time course curve in patients with moyamoya disease by using the relative recirculation (rR) parameter. Our aims were to increase understanding of the rR parameter and to assess its possible value in the investigation of moyamoya disease. METHODS Six patients with confirmed moyamoya disease and five normal participants were examined by using dynamic T2*-weighted MR perfusion imaging. Parametric maps of relative cerebral blood volume, time to peak (TTP), and rR were calculated. The width of the normal distribution of TTP and the normal upper limit for rR were derived from the normal participants by identification of the 97.5% confidence limits for the distributions. Major vessels were identified by selection of pixels with relative cerebral blood volume >0.5. Areas of abnormally prolonged TTP and of increased rR were then identified in patients, and the relationship between these parameters and major vessels was examined. RESULTS The combination of cerebral blood volume >50%, elevated TTP, and elevated rR values accurately identified areas of moyamoya vessel formation seen on angiograms. Larger well-developed meningeal and basal collaterals did not show abnormalities of rR. Areas of prolonged TTP were also observed to occur in the brain distal to arterial occlusion in all cases. In three of these, abnormal elevation of rR was observed in the center of regions of prolonged TTP. CONCLUSION These findings support those of our previous work, which suggested that rR can act as an indicator of regional microvascular abnormality, such as that seen in areas of angiogenic activity. They also suggest that measurement of rR may provide valuable additional information regarding patients with moyamoya disease.