Sequential PET estimation of cerebral oxygen metabolism with spontaneous respiration of 15O-gas in mice with bilateral common carotid artery stenosis.

Positron emission tomography with 15O-labeled gases (15O-PET) is important for in vivo measurement of cerebral oxygen metabolism both in clinical and basic settings. However, there are currently no reports concerning 15O-PET in mice. Here, we developed an 15O-PET method applicable to mice with spontaneous respiration of 15O-gas without a tracheotomy catheter. Sequential 15O-PET was also performed in a mouse model of chronic cerebral hypoperfusion with bilateral common carotid artery stenosis (BCAS) induced by placement of microcoils. 15O-gas with isoflurane was supplied to the nose of mouse with evacuation of excess 15O-gas surrounding the body. 15O-PET was performed on days 3, 7, 14, 21, and 28 after surgery. Cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen (CMRO2) were calculated in whole brains. A significant decrease in CBF and compensatory increase in OEF in the BCAS group produced CMRO2 values comparable to that of the sham group at three days post-operation. Although CBF and OEF in the BCAS group gradually recovered over the first 28 days, the CMRO2 showed a gradual decrease to 68% of sham values at 28 days post-operation. In conclusion, we successfully developed a noninvasive 15O-PET method for mice.