Abstract
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Objectives: Respiratory motion during PET/CT studies affects the quantification of lesion volume and activity uptake. We present a new method of motion correction in a limited area around the tumor to reduce these effects. In this method all acquired counts are used for the resulting image so that the signal to noise ratio is not reduced compared to the uncorrected images. Methods: PET data of a motion-phantom study (1 hot spot 22 mm diameter with background activity) and for 5 patients with single, separable lung lesions were acquired in list-mode format (Siemens Biograph 16). The data were divided retrospectively in 16 gates, which was found to be the optimal number, corresponding to the simulated respiratory cycle or the one of the patient, which has been registered with a pressure sensitive belt (Anzai Med.). Images for these gates were reconstructed as well as an average image of the whole acquisition. The movement of the lesion between the gates was registered by a center of mass (COM) approach within a manually drawn volume of interest (VOI). Subsequently the voxels in the VOI were shifted for each gate according to the difference of the COM between this gate and the reference gate (end expiration). Afterwards the images of all gates were summed. Lesion size and maximum activity uptake in non-corrected and corrected images were compared. Results: In the phantom study, the volume of the hot spot in corrected data was reduced up to 5%, 14% and 38% for motion amplitudes of 5 mm, 15 mm and 30 mm, and reached the value without movement within 11%. Activity uptake increased up to 1%, 5% and 11%, representing the true value within 8%. In patients tumor volume of the corrected images was up to 37% smaller than in the uncorrected ones, while the activity uptake was increased up to 27% in the corrected data. Conclusions: The proposed method improves the correct quantification of lesions in an area with strong respiratory movement without decreasing the image quality or increasing the acquisition time which is the case for respiratory gated studies. Especially when using PET data for radiotherapy planning the patient will benefit from a more precise tumor definition.
- Society of Nuclear Medicine, Inc.