Functional Magnetic Resonance Imaging Indices as Predictors of Cerebral Perfusion and Functional Changes after Carotid Intervention

Patients with critical extracranial carotid stenosis often benefit from carotid interventions such as carotid angioplasty with stenting (CAS) to prevent subsequent ischemic events. Hyperperfusion syndrome, defined as an increase in ipsilateral cerebral blood flow (CBF) that far exceeds the metabolic demands of brain tissue following recanalization of carotid stenosis, is one of the major complications of CAS. Once happened, it usually causes disastrous outcome, e.g. unilateral headache, seizures, and intracerebral hemorrhage. Several factors including age, extremely critical carotid stenosis, peri-operative hypertension, and poor collateral circulation of brain are thought to be related to hyperperfusion syndrome. Perfusion indices, such as CBF, mean transit time and time-to-peak, derived from CT or MRI scans, have previously been showed to correlate with hyperperfusion following CAS. However, they were not directly related to pathological conditions of blood vessels. Recent development of advanced MRI techniques allows producing image contrast reflecting attributes of vessel physiology and microstructure. Among them, dynamic contrast enhanced MRI, gives access to information on vessel permeability, vessel size and tracer transit time, which are of importance for the diagnosis and therapeutic follow-up of various brain pathologies. In addition, blood oxygenation level-dependent (BOLD) MRI can be applied in studies of brain functions as well as the vasomotor response. We hypothesize that MRI of impaired morphometry and function of small vessels is predictive for the hyperperfusion syndrome thus may play important roles in predicting the perfusion outcome after the carotid intervention. Therefore this proposed study aims to evaluate the relationships between the baseline functional MRI indices, including (1) cerebral vasoreactivity (CVR), (2) vessel permeability, (3) microvessel size and (4) tracer transit times, and the CBF changes in patients receiving CAS. And subsequently, we try to find out if those imaging indices or combinations of them could be useful parameters in patient selection or predicting the prognosis of CAS. In addition to the hyperperfusion problem, cognitive impairment due to inferior regional perfusion and the possibility of recovery after CAS are important clinical issues. Currently the clinical cognitive assessment usually leads to significant variation which makes subjective evaluation of cognitive impairment difficult, as well as the prediction of the recovery. In the recently years, resting-state fMRI has been developed as an important tool for studying functional connectivity of the brain. Since functional connectivity should play an important role in the recovery of cognitive functions, we also plan to incorporate both cognitive assessment and resting-state fMRI before and after the CAS and study their correlations with perfusion impairment. We aim to understand the interplay between this advanced imaging technique, perfusion and cognitive functions, and hope to use the information of functional connectivity to help predicting cognitive recovery of patients after the CAS.

Project ID:PC9907-2512
External Project ID:NSC99-2628-B182-028-MY2