PET technique reduces motion artifacts in brain imaging

A technique using a commercially available optical tracking system helps counter motion artifacts in neurological PET studies, according to a study published in the June issue of the Journal of Nuclear Medicine.

Brain PET examinations are lengthy, making head motion inside the scanner inevitable. This leads to poor resolution, if not erroneous data interpretation. Several schemes for motion correction have been proposed with varied degrees of success. But most have been tested only on phantoms or non-neurological studies.

Australian and German investigators assessed motion artifact correction in six human subjects undergoing PET scanning of neuroreceptor binding. They used a multiple-acquisition frame (MAF) method supported by a motion-tracking system that targets special body markers with infrared light. These markers are attached to a cap or gogglelike accessory that covers the patient's skull during scanning.

The MAF-based motion correction method successfully reduced blurry PET images and statistical noise from parametric maps, which involve data analysis charts displayed along with serial FDG-PET images.

The researchers monitored the effect of motion on parametric images of the brain's distribution volume ratio (DVR), a noninvasive method to look into the diagnosis and management of psychiatric disorders. DVR images correlate with the binding potential of the receptor ligand F-18 altanserin.

DVR images of F-18 altanserin PET scans showed a number of movement-related artifacts that appeared as discontinuities and small spots at the border between gray and white matter and at the outer border of gray matter. MAF eliminated all of these artifacts.

The MAF technique consists of short time frames recombined into a longer, motion-corrected sequence. But MAF isn't perfect. Neither coregistration nor scatter correction can take place if the time frames are too short. And the technique can make scanning and interpretation time-consuming. Further studies should examine the pros and cons of the MAF and similar methods and their impact on the interpretation of parametric PET images, the researchers said.

The motion-tracking device used in combination with motion-correction software and parametric DVR helped to improve brain PET considerably and to avoid calculation errors that are likely to occur using conventional methods, they said.

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