Impact of extraneous mispositioned events on motion-corrected brain SPECT images of freely moving animals

SPECT imaging of freely moving small animals would allow monitoring of many important physiological processes and behaviours, which are normally inhibited by anaesthetic drugs. However, in a freely moving animal it may be difficult, if not impossible, to distinguish between events that originate in the head from those that originate in the body and motion parameters cannot be assumed to be the same for the head and the body. This work employs a Monte CaIro simulation, based on a singleheaded SPECT camera, to assess the impact of inaccurate motion compensation of events originating in the body of a realistic mouse phantom, on the accuracy of motion corrected brain images. Results on non-attenuated data showed minimal motion-related bias <; 1 %) in regions such as the striatum and the lacrimal glands, but increased bias (2-5%) in the cerebellum, which is closer to the extraneous compartment. Simulations on attenuated data showed higher bias in all regions (10-20%) caused by the inaccurate attenuation correction, due to the fact that the pose of the body is unknown. Also it appears that thee geometry of the detector (i.e. rotating vs. full ring), as well as the energy of the photons have an impact on the accuracy of the motion and attenuation corrected mouse brain. Future work will investigate the impact of these effects on the accuracy and precision of the end-point kinetic parameters of an ¹²⁵I dynamic SPECT scan.