Human cerebral metabolic study using 13N-labeled ammonia on carotid artery endarterectomy

Objectives Carotid artery plaque is a leading cause of ischemic stroke and carotid endarterectomy (CEA) is one of major treatment methods for it. Cerebral metabolism change is unclear after CEA in human subjects. This study is to evaluate effect of cerebral ammonia metabolism after CEA using 13N-labelled ammonia PET in human.

Methods 21 patients were enrolled with a mean age of 59.5 year old:16 males and 5 females. 5 patients underwent right and 6 left CEA. Carotid artery stenosis in 11 patients was over 80%, using ultrasound before CEA. 13N-labelled ammonia (137 MBq) PET scanning was performed two times (before and after CEA operation) for everyone patient. The first ammonia PET scanning was performed one day before CAE, the second PET scanning was performed between one and four weeks after CAE. After injection of 13N-labelled ammonia, static PET data was acquired for 10 minutes. Region of interest (ROI) covering major cerebral hemisphere was drawn and ammonia uptake in ROI was taken into account for ipsilateral and contralateral hemisphere using Carimas2 (a PET analysis package developed in Turku PET Centre of Finland).

Results No hyperperfusion syndrome was observed in all patients after CAE. No significant change of cerebral hemisphere ammonia uptake was found between ipsilateral and contralateral hemispheres before CAE (ratio=0.98, p<0.01) and after CAE (ratio=1.09, p<0.01). Ammonia uptake in both ipsilateral and contralateral hemispheres decreased significantly after CAE, ipsilateral and contralateral uptake decreased to 23.2% and 23.5% after CAE, respectively.

Conclusions Using 13N-labeled ammonia PET after CEA for patients with severe carotid artery stenosis, this study revealed uptake of ammonia in both ipsilateral and contralateral hemispheres is decreased significantly. Moreover, no significant difference of ammonia uptake between two hemispheres is found preoperatively and postoperatively, respectively.