María Hernández Pérez
Until recently, conventional angiography has been the only technique able to give information about the dynamic status of the intracranial vessels. Despite different CT and MR techniques that have been developed to assess the grade of collateral circulation after a cerebral arterial occlusion, we found that the great majority of these methods lacked information about changes in the blood flow over time and could be prone to error due to its static nature. Because of the importance of the hemodynamic changes of the intracerebral circulation during acute ischemic stroke, we were interested in developing a noninvasive method that would allow evaluation of these changes.
Dynamic MR angiography (dMRA) is a T1 gadolinium-enhanced dynamic sequence that assesses blood flow over time. Mainly used in arteriovenous malformations and brain and neck tumors, dMRA provides DSA-like hemodynamic information and has a very fast acquisition time of around 70 seconds. With these features, we thought that this sequence could be an ideal candidate to develop our research. For the purpose of testing the performance of dMRA in detecting site of occlusion and collateral assessment in acute ischemic stroke, 25 patients with proximal anterior circulation occlusion within 12 hours of symptom onset underwent dMRA on a 3T scanner. DWI, PWI, TOF imaging, and dMRA were performed. dMRA was more accurate than TOF in identifying tandem occlusions and allowed us to detect forward flow through the thrombus that was undetected with TOF imaging. Furthermore, we observed that a complete and fast collateral filling on dMRA was associated with smaller DWI lesion volume, smaller hypoperfused volume, and lower severity of the hypoperfusion. Finally, patients with symmetrical clearance of transverse sinuses were more likely to have complete collateral filling.
The main advantages of the dMRA are that it does not need further postprocessing and permits visualization in a fast and direct way of the site of the occlusion, the degree and velocity of the arterial collateral circulation, as well as the venous drainage.