Monitoring Head Movement in a Brain PET Scanner

Abstract

When acquiring PET images, body motions are unavoidable, given that the acquisition time could last 10-20 minutes or more. These motions can seriously deteriorate the quality of the final image at the level of image reconstruction and attenuation corrections. Movements can have rhythmic patterns, related to respiratory or cardiac motions, or they can be abrupt reflexive actions caused by the patient's discomfort. Many approaches, software and hardware, have been developed to mitigate this problem where each approach has its own advantages and disadvantages. In this work we present a simulation study of a head monitoring device, named CrowN@22, intended to be used in conjunction with a dedicated brain PET scanner. The CrowN@22 device consists of six point sources of non-pure positron emitter isotopes, such as 22Na or 44Sc, mounted in crown-like rings around the head of the patient. The relative positions of the point sources are predefined and their actual position, once mounted, can be reconstructed by tagging the extra 1274 keV photon (in the case of 22Na). These two factors contribute to a superb signal-to-noise ratio, distinguishing between the signal from the 22Na monitor point sources and the background signal from the FDG in the brain. Hence, even with a low activity for the monitor point sources, as low as 10 kBq per point source, in the presence of 75 MBq activity of 18F in the brain, one can detect brain movements with a precision of less than 0.3 degrees, or 0.5 mm, which is of the order of the PET spatial resolution, at a sampling rate of 1 Hz.