The difficulties and the expense associated with the use of external measuring devices have resulted in an increased focus on data-driven methods for PET motion correction.
However, key issues exist related to device cost, service, maintenance, and more. 5 presented methods using external devices. Dawood et al., 2 Qiao et al., 3 Lamare et al., 4 and Liu et al. The current clinical standard uses external measuring devices to extract respiratory signals from the patient. 1 Respiratory motion is particularly problematic for PET due to typical scan times of 2–5 min (8–20 min for whole-body scans), leading to averaging of the image pixel values across the range of motion. Along with blurring and otherwise degraded image quality, motion artifacts may result in inaccurate localization of lesions, miscalculation of standardized uptake values (SUVs), and overestimation of tumor size and involvement. Motion artifacts caused by the natural breathing of the patient during a scan are a major concern. Positron emission tomography (PET) is a noninvasive imaging modality widely used in clinical application to study organ and tissue function and is used most often in conjunction with computed tomography (CT) to acquire anatomical information and for emission data correction. The algorithm has the potential to facilitate true motion correction where the reconstruction algorithm can use all data available. Gating based on the motion estimate is shown to quantifiably improve the image quality in both a controlled point source phantom study and in clinical data patient studies. ConclusionĪ PEPT- based algorithm has been presented for determining movement due to respiratory motion during PET/CT imaging. In addition, max SUVs were found to be 4–10% higher in the TOF-PEPT-based gated images than in those based on Anzai and COM methods. The distinct presence of lesions with reduced blurring effect and generally sharper images were readily apparent in all clinical studies. In comparison with the ungated image, a 14–39% increase in the max SUV across several lesion areas and an 8.7% increase in the max SUV on the tracked lesion area were observed in the gated images based on TOF-PEPT. Maximum Standardized Uptake Values (SUVs) were used to quantitatively compare the reconstructed-gated images. TOF-PEPT was found to be 13–38% better correlated with the Anzai results than the COM methods. The derived motion signals correlated well with the Anzai band correlation coefficients of 0.99 and 0.94-0.97 were obtained for the phantom study and the clinical studies, respectively. The TOF-PEPT algorithm is shown to successfully determine the respiratory motion for both phantom and clinical studies. Using the motion estimate from each method, amplitude-based gating was applied, and gated images were reconstructed. For the purposes of additional comparison, a center-of-mass (COM) algorithm was implemented both with and without the use of TOF information. The extracted motion signals were compared with the Anzai band when applicable. The motion tracking was performed using a preselected region of interest (ROI), manually drawn around point sources or lesions on reconstructed images. For studies with radioactive point sources, they were placed on patients during PET/CT imaging. The TOF-PEPT algorithm was implemented and investigated under different scenarios: (a) a phantom study with a point source and an Anzai band for respiratory motion tracking (b) a phantom study with a point source only, no Anzai band (c) two clinical studies with point sources and the Anzai band (d) two clinical studies with point sources only, no Anzai band and (e) two clinical studies using lesions/internal regions instead of point sources and no Anzai band. This paper introduces a time-of-flight (TOF)-weighted positron emission particle tracking (PEPT) algorithm that facilitates lesion-specific respiratory motion estimation from raw listmode PET data. Data-driven techniques are an active area of research with limited exploration into lesion-specific motion estimation. Hardware-based motion estimation, which is the current clinical standard, requires initial setup, maintenance, and calibration of the equipment, and can be associated with patient discomfort.
Respiratory motion of patients during positron emission tomography (PET)/computed tomography (CT) imaging affects both image quality and quantitative accuracy.
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