Semiconductor PET demonstrated metabolic suppression in red nucleus in patients with crossed cerebellar diaschisis

Objectives Red nucleus (RN) coordinates with contralateral cerebellum thus is a structure responsible for movement disorders. However, little is known about the clinical importance of RN in human, due to its small size limiting functional assessments in-vivo. The high spatial resolution of semiconductor PET (sPET) may conquer the limitation and allow metabolic activity measurements. The purpose of this study was to investigate glucose metabolism of RN using sPET in glioma patients with crossed cerebellar diaschisis (CCD), who were expected to show metabolic suppression in RN.

Methods This study included 31 patients (M:F=19:12, 49±14 years old) with cerebral glioma. Tumors involving brain stem or cerebellum were excluded. One hour after injection of 400 MBq of FDG, 30 min of sPET (Hitachi Ltd.) scanning was started in 3D acquisition mode. The sPET covers 24 cm of z-axial and 31 cm of transaxial field of view with intrinsic spatial resolution of 2.3 mm FWHM. Images were reconstructed with maximum a posteriori and coregistered with MRI. SUVmax of RN, SUVmean of background (BG), and SUVmean of cerebellar hemisphere were investigated. CCD was defined as asymmetry index (AI) > 0.05.

Results RN was successfully visualized at least in contralateral side of tumor as a higher activity than the BG midbrain (RN/BG ratio=1.29±0.09). Overall, SUVs of ipsilateral RN and contralateral cerebellum were closely correlated (R=0.89, P<0.001). In 21/31 (68%) cases showing CCD, SUVmax in RN of ipsilateral side was lower than that in RN of contralateral side (5.89±1.22 vs 6.42±1.45, AI=-0.08±0.07, p<0.01), while no significant difference was observed between two sides in remaining 10 patients without CCD (7.37±1.24 vs 7.41±1.05, AI=0.00±0.17, P=NS).

Conclusions The sPET successfully assessed metabolic activity of RN in all the patients, and demonstrated metabolic correlation between ipsilateral RN and contralateral cerebellum in patients with CCD. The high spatial resolution of sPET allows functional imaging of RN