Optimised Motion Tracking for Positron Emission Tomography Studies of Brain Function in Awake Rats

Abstract

Positron emission tomography (PET) is a non-invasive molecular imaging technique using positron-emitting radioisotopes to study functional processes within the body. High resolution PET scanners designed for imaging rodents and non-human primates are now commonplace in preclinical research. Brain imaging in this context, with motion compensation, can potentially enhance the usefulness of PET by avoiding confounds due to anaesthetic drugs and enabling freely moving animals to be imaged during normal and evoked behaviours. Due to the frequent and rapid motion exhibited by alert, awake animals, optimal motion correction requires frequently sampled pose information and precise synchronisation of these data with events in the PET coincidence data stream. Motion measurements should also be as accurate as possible to avoid degrading the excellent spatial resolution provided by state-of-the-art scanners. Here we describe and validate methods for optimised motion tracking suited to the correction of motion in awake rats. A hardware based synchronisation approach is used to achieve temporal alignment of tracker and scanner data to within 10 ms. We explored the impact of motion tracker synchronisation error, pose sampling rate, rate of motion, and marker size on motion correction accuracy. With accurate synchronisation (<100 ms error), a sampling rate of >20 Hz, and a small head marker suitable for awake animal studies, excellent motion correction results were obtained in phantom studies with a variety of continuous motion patterns, including realistic rat motion (<5% bias in mean concentration). Feasibility of the approach was also demonstrated in an awake rat study. We conclude that motion tracking parameters needed for effective motion correction in preclinical brain imaging of awake rats are achievable in the laboratory setting. This could broaden the scope of animal experiments currently possible with PET.

Mapping Changes in Mouse Brain Metabolism with PET/CT

“…It is nevertheless clear that with appropriate environmental control, 18 F-FDG imaging can be exploited in cognitively active animals for both tumor imaging (32) and the detection of metabolism in performance-related brain centers (38)(39)(40), strongly supporting the notion that behavioral control after 18 F-FDG administration may indeed increase the homogeneity of absolute radioactivity in the brain.…”

Tracking and characterizing the head motion of unanaesthetized rats in positron emission tomography

“…In Emmi et al [20] and Crescimanno et al [21], rats with specific brain lesions were found to execute single-axis head turns with a maximum speed of 130 deg s 21 . The study of Jobbagy et al [22] reported head location and direction measurements of rats housed in inclined tubes, but the temporal resolution of the measurements (250 ms) was not suitable for assessing instantaneous speed [23].…”

Quantification of local reconstruction accuracy for helical CT with motion correction

“…I N PET brain imaging, rigid motion correction can be obtained based on pose measurement using optical motion tracking [1], [2]. Previously we have applied a similar rigid motion correction technique to helical CT brain scans, by measuring the head motion with a Polaris system (Spectra, Northern Digital Inc., Waterloo, Canada) [3], [4].…”