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This study was undertaken to correct for motion artifacts in dynamic breast F-18-FDG PET/CT images, to improve
differential-image quality, and to increase accuracy of time-activity curves. Dynamic PET studies, with subjects prone,
and breast suspended freely employed a protocol with 50 frames, each 1-minute long. A 30 s long CT scan was acquired
immediately before the first PET frame. F-18-FDG was administered during the first PET time frame. Fiducial skin
markers (FSMs) each containing ~0.5 &mgr;Ci of Ge-68 were taped to each breast. In our PET/PET registration method we
utilized CT data. For corresponding FSMs visible on the 1st and nth frames, the geometrical centroids of FSMs were
found and their displacement vectors were estimated and used to deform the finite element method (FEM) mesh of the
CT image (registered with 1st PET frame) to match the consecutive dynamic PET time frames. Each mesh was then
deformed to match the 1st PET frame using known FSM displacement vectors as FEM loads, and the warped PET timeframe
volume was created. All PET time frames were thus nonrigidly registered with the first frame. An analogy
between orthogonal components of the displacement field and the temperature distribution in steady-state heat transfer in
solids is used, via standard heat-conduction FEM software with "conductivity" of surface elements set arbitrarily
significantly higher than that of volume elements. Consequently, the surface reaches steady state before the volume. This
prevents creation of concentrated FEM loads at the locations of FSMs and reaching incorrect FEM solution. We observe
improved similarity between the 1st and nth frames. The contrast and the spatial definition of metabolically hyperactive
regions are superior in the registered 3D images compared to unregistered 3D images. Additional work is needed to
eliminate small image artifacts due to FSMs.
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