Visualization of small brain nuclei with a high-spatial resolution, clinically available whole-body PET scanner

Area of Science:

• Nuclear Medicine
• Radiology
• Neuroimaging

Background:

• Physiological 18F-fluorodeoxyglucose (18F-FDG) uptake in small brainstem nuclei is challenging to visualize with standard PET scanners.
• Whole-body (WB) silicon photomultiplier positron emission tomography (SiPM-PET) scanners offer improved sensitivity and resolution.

Purpose of the Study:

• To evaluate the visibility of 18F-FDG uptake in brainstem nuclei using a WB SiPM-PET scanner.
• To determine the optimal number of iterations for ordered-subset expectation maximization (OSEM) reconstruction with time-of-flight (TOF) and point-spread function (PSF) for enhanced visualization.

Main Methods:

• Ten healthy subjects underwent 18F-FDG PET/CT and brain MRI.
• PET images were reconstructed using OSEM with 4, 16, 64, and 256 iterations, combined with TOF and PSF.
• MR-coregistered PET images were analyzed for 18F-FDG uptake visibility in various brainstem nuclei.

Main Results:

• Iteration 64 demonstrated the best visualization of 18F-FDG uptake in most brainstem nuclei, including the inferior olivary nuclei, midbrain raphe nuclei, and lateral/medial geniculate nuclei.
• Iteration 64 clearly visualized FDG accumulation in 98 out of 100 assessed structures.
• Other iterations showed varying degrees of visibility, with iteration 16 being optimal for the dentate nuclei and red/subthalamic nuclei.

Conclusions:

• Clinically available WB SiPM-PET scanners are effective for visualizing physiological 18F-FDG uptake in small brain nuclei.
• Sufficiently high iteration numbers (e.g., 64) in OSEM reconstruction with TOF and PSF are crucial for optimal image quality and diagnostic utility.