Fast motion tracking of radioactive markers for motion correction of awake and unrestrained rat brain PET

Due to the confounding factors of anesthesia and stress in rats, methods to perform brain PET scans of awake and unrestrained rats are being developed. In one of these techniques the motion of the rat head must be measured during the scan to correct the PET data afterwards. We propose to measure the head motion directly from the list-mode PET data itself by using positron-emitting point sources attached to the rat head. The point sources are tracked in image space in short time frames (32 ms). The tracking was validated with a scan of a manually moved microDerenzo resolution phantom and an in-vivo [18F]FDG awake rat brain scan. The phantom was successfully tracked using 3 point sources. The motion information was used for motion correction of the PET data and the 1.5 mm diameter rods were recovered after correction. The rat head was effectively tracked during the awake scan using 4 point sources. Image quality was similar to a static reference scan and different brain regions, such as cortex, hypothalamus and cerebellum could be identified after motion correction. The average regional uptake difference between the motion corrected and static reference scan was 3.7%. The proposed tracking is thus an effective tool for motion tracking for head motion compensation in awake rat scans. In particular this method does not rely on large optical markers that need to be attached to the rat head, avoids the need for spatiotemporal calibration between an optical tracking device and the PET scanner, and finally is ideally suited to be used in PET scanners with small scanner bore size where optical tracking is challenging.