An illustration of event-by-event motion correction during reconstruction. LOR i k generated at (x,y,z) during inspiration, is transformed to a reference location, i.e., end-expiration (x1,y1,z1) where the attenuation CT was acquired, as LOR .
The work flow of INTEX3D and MOLAR reconstruction.
(a) Illustration of the NEMA phantom setup placed on the QUASAR motion platform. The bold arrows indicate the displacement in each direction. (b) The respiratory trace used to drive the QUASAR motion platform. The first 180 s data are shown here.
Reconstructed images of the NEMA phantom in transaxial, coronal, and sagittal views. Images in each row are the central slices that cut through the smallest sphere in that view. The axis in the first row indicates the directions of the respiration motion in that view. (a) The static acquisition. The acquisition with motion and reconstructed with (b) NMC, (c) The end-expiration gate of eight-bin phase gating, (d) INTEX1D, and (e) INTEX3D.
The maximum intensity projection in coronal view of the segmentations of the left kidney (top) and pancreas (bottom) across eight respiratory gates from a sample subject with [18F]FP(+)DTBZ. The horizontal lines above and under each organ reveal the magnitude of organ displacement across eight gates.
The linear correlations between the center of mass (COM) of the (a) pancreas and (b) kidney with Anzai mean displacement derived from eight respiratory gates of a sample human study. The correlation in the LR direction was small since the motion in that direction was negligible and its correlation with the external trace was poor. The numbers denote the corresponding gating phase where gates 5 and 8 were the end-expiration and inspiration gates, respectively.
Reconstructed images in the coronal view of the pancreas study with [18F]FP(+)DTBZ from three healthy subjects with NMC, gated image at end-expiration phase, INTEX1D, INTEX3D, and INTEX3D with AMNLM postfiltering. The arrows indicate that the blurring caused by respiratory motion in pancreas has been recovered by INTEX3D without increasing noise. The further application of AMNLM on the INTEX3D images suppressed noise effectively while preserving boundaries and fine structures. Images in each row are displayed in the same intensity scale.
Reconstructed images in the coronal view at the level of the kidneys for the same subjects as shown in Fig. 7 . The arrows indicate the blurring on the kidney cortex caused by respiratory motion that was effectively corrected by INTEX3D. Images in each row are displayed in the same intensity scale.
Comparisons of gated images in the coronal view (same locations at the pancreas and kidney as the images shown in Figs. 7 and 8 ) without intragate motion correction, and with event-by-event intragate motion correction (INTEX3D) at end-expiration and inspiration phases. All the images were postsmoothed with a 3D Gaussian filter with 4 mm FWHM. It can be seen that the differences between NMC and INTEX3D are subtle at end-expiration gate but are substantial at inspiration phase (as denoted by the arrows) due to the larger amount of intragate motion during inspiration.
Time-activity-curves measured in the pancreas and kidney of subject 1 from the first 10 min scan with NMC and INTEX3D. It can be seen that the tracer concentration increased by 18% in the pancreas and 11% in the kidney at the maximum of the curves after correcting for respiratory motion using INTEX3D.
Sample slices of the FMISO study in transaxial (top) and coronal (bottom) views. The arrows indicate three lesions (L1–L3) in the lung. All images are displayed in the same intensity scale.
CRC of the NEMA phantom study. The percentage changes compared to the static acquisition are shown in the parentheses.
Motion amplitudes of three subjects for [18F]FP(+)DTBZ measured from the centroids of the pancreas.
The slopes of the regression lines obtained from INTEX for three [18F]FP(+)DTBZ subjects in AP and SI directions. The LR is not shown as the correlation in that direction was small.
Percentage change of the mean activity in the pancreas compared to NMC.
Percentage change of the mean activity in the kidneys compared to NMC.
Percentage change of the noise level (standard deviation) in the liver VOI compared to NMC.
The L/B ratio and standard deviation in the blood pool comparing to NMC of the FMISO study. The percentage changes comparing to NMC are shown in the parentheses.
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