Correction of head movement by frame-to-frame image realignment for receptor imaging in positron emission tomography studies with [11C]raclopride and [11C]FLB 457
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Positron emission tomography (PET) scans of imaging receptors require 60–90-min dynamic acquisition for quantitative analysis. Head movement is often observed during scanning, which hampers the reliable estimation of quantitative parameters. This study evaluated image-based motion correction by frame-to-frame realignment for PET studies with [11C]raclopride and [11C]FLB 457 acquired by an Eminence SET-3000GCT/X and investigated the effect of this correction on the quantitative outcomes.
First, an optimal method for estimating motion parameters was evaluated by computer simulation. Simulated emission sinograms were reconstructed to the PET images with or without attenuation correction using a µ-map of the transmission scan. Six motion parameters were estimated frame-by-frame by registering each frame of the PET images to several types of reference images and the reliability of registration was compared. Next, in [11C]raclopride and [11C]FLB 457 studies in normal volunteers, six motion parameters for each frame were estimated by the registration method determined from the simulation results. Head movement was corrected by realigning the PET images reconstructed with a motion-included µ-map in which a mismatch between the transmission and emission scans was corrected. After this correction, time-activity curves (TAC) for the striatum or cerebral cortex were obtained and the binding potentials of the receptors (BPND) were estimated using the simplified reference tissue model.
In the simulations, the motion parameters could be reliably estimated by registering each frame of the non-attenuation-corrected PET images to their early-phase frame. The motion parameters in the human studies were also obtained using the same method. After correction, a discontinuity of TACs in the striatum and cerebral cortex was remarkably improved and the BPND values in these regions increased. Compared to the motion-corrected PET images reconstructed using the measured µ-map, the images reconstructed using the motion-included µ-map did not result in a remarkable improvement of BPND in the striatum of [11C]raclopride studies, while the BPND in the cerebral cortex changed in some [11C]FLB 457 studies in which large head movement was observed.
In PET receptor imaging, head movement during dynamic scans can be corrected by frame-to-frame realignment. This method is easily applicable to clinical studies and provides reliable TACs and BPND.
KeywordsPET receptor imaging Head movement Image realignment Attenuation correction Binding potential
We thank the staff of the clinical research support section, the clinical neuroimaging team, and the radiopharmaceutical production team at the National Institute of Radiological Sciences QST for their assistance in conducting the PET studies and Dr. Keisuke Matsubara at the Research Institute for Brain and Blood Vessels Akita for his suggestion regarding the image analysis. We also thank Drs. Keishi Kitamura and Tetsuro Mizuta at the Shimadzu Corporation for their support in the data processing of the reconstruction.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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