Whole-body motion correction in cardiac PET/CT using Positron Emission Tracking: A phantom validation study

A whole-body motion correction algorithm that is based on positron emission tracking (PeTrack) of fiducial markers has been validated using phantom studies in PET/CT. Patient motion during medical imaging procedures is an inevitable source of artifact and image quality reduction. A motion correction algorithm has been designed to reduce the adverse effects of misalignment artifacts between the CT attenuation map and PET data as well as reduction of spatial resolution associated with motion blurring. A phantom with a left-ventricular cardiac insert was imaged for 5 minutes in list-mode format on a GE Discovery 690 PET/CT scanner. Four acquisitions were completed in total: one without motion and three with motion in the superior-inferior and lateral directions. The list-mode data were processed offline using the PeTrack algorithm to generate 3D motion traces of a 30 kBq Na-22 fiducial marker placed on the anterior surface of the phantom. Whole-body motion triggers were created when a change in marker position, relative to t = 0, exceeded a voxel length in any direction. Motion data were used to rigidly align CT and raw emission data prior to reconstruction as well as align reconstructed PET motion frames. Images with and without motion correction were compared to the static reference image to evaluate changes in apparent left-ventricular (LV) wall-thicknesses, signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR). With respect to the Reference image, Non-Corrected images exhibited average increases in LV wall-thickness in the range of 9-55%, SNR reductions from 31-63% and CNR reductions of 27-80%. Motion corrected images exhibited average changes in LV wall-thickness of -0.2-6%, SNR reductions of 4-10% and CNR reductions of 13-35%. The authors concluded that motion tracking data acquired using PeTrack can be incorporated into the reconstruction algorithm to correct for rigid motion and significantly reduce the degrading factors of whole-body motion in PET/CT

Whole-body motion correction in 13N-ammonia myocardial perfusion imaging using positron emission tracking

Patient motion during positron emission tomography (PET) studies leads to degradation of image quality. Not only does patient motion lead to blurring of regions of tracer uptake but it can also lead to mis-alignment artifacts associated with spatial mis-registration between the emission and transmission data used for attenuation correction. In this study we examine the benefits of a three-dimensional whole-body motion correction algorithm based on the use of tracking external radioactive markers placed on the patient. We used the positron emission tracking (PeTrack) algorithm to estimate translational patient motion for three patients who underwent 13N-ammonia myocardial perfusion imaging studies at rest and stress. PeTrack was used to identify instances of whole-body patient motion and its extent with respect to a reference position. This information was used to bin the raw list-mode data based on patient-motion amplitudes. The resulting set of gated emission data were reconstructed after using the PeTrack data to rigidly align the attenuation image to each gate. The final set of images were then re-aligned to the reference position. The weighted average of the individual gated images produces the final motion-corrected static image. This approach was evaluated by comparing the relative perfusion in the three arterial regions of the left-ventricular (LV) polar maps. Additionally, regional LV wall thickness and blood pool volume were measured. Whole-body motion in this small sample was limited and largely returned to the reference position. When considering rest and stress acquisitions, no statistically significant differences were observed for any of the metrics. LV wall thicknesses were significantly reduced after motion correction for the stress cases which exhibited the greatest motion. The benefits of motion correction may not be realized unless the extent of whole-body patient motion is large and/or non-returning. Our study demonstrated successful motion tracking using PeTrack, but this work must be extended to include more cases with more severe motion is indicated

Clinical comparison of the positron emission tracking (PeTrack) algorithm with the real-time position management system for respiratory gating in cardiac positron emission tomography

Purpose: A data-driven motion tracking system was developed for respiratory gating in positron emission tomography (PET)/computed tomography (CT) studies. The positron emission tracking system (PeTrack) estimates the position of a low-activity fiducial marker placed on the patient during imaging. The aim of this study was to compare the performance of PeTrack against that of the real-time position management (RPM) system as applied to respiratory gating in cardiac PET/CT studies. Methods: The list-mode data of 35 patients that were referred for 82Rb myocardial perfusion studies were retrospectively processed with PeTrack to generate respiratory motion signals and triggers. Fifty acquisitions from the initial cohort, conducted under physiologic rest and stress, were considered for analysis. Respiratory-gated reconstructions were performed using reconstruction software provided by the vendor. The respiratory signals and triggers of the gating systems were compared using quantitative measurements of the respiratory signal correlation, median, and interquartiles range (IQR) of observed respiratory rates and the relative frequencies of respiratory cycle outliers. Quantitative measurements of left-ventricular wall thicknesses and motion due to respiration were also compared. Real-time position management signals were also retrospectively processed using the trigger detection method of PeTrack for a third comparator (“RPMretro”) that allowed direct comparison of the motion tracking quality independently of differences in the trigger detection methods. The comparison of PeTrack to the original RPM data represent a practical comparison of the two systems, whereas that of PeTrack and RPMretro represents an equal comparison of the two. Nongated images were also reconstructed to provide reference left-ventricular wall thicknesses. LV wall thickness and motion measurements were repeated for a subset of cases with motion ≥7 mm as image artifacts were expected to be more severe in these cases. Results: A significant correlation (P < 0.05) was observed between the RPM and PeTrack respiratory signals in 45/50 acquisitions; the mean correlation coefficient was 0.43. Similar results were found between PeTrack and RPMretro. No significant difference was observed between the RPM and PeTrack with respect to median respiratory rates and the percentage of respiratory cycles outliers. Respiratory rate variability (IQR) was significantly higher with PeTrack vs RPM (P = 0.002) and RPMretro (P = 0.04). Both PeTrack and RPM had a significant increase in the percentage of respiratory rate outliers compared to RPMretro (P < 0.001 and P = 0.001, respectively). All methods indicated significant differences in LV thickness compared to nongated images (P < 0.02). LV thickness was si

Evaluation of the clinical efficacy of the PeTrack motion tracking system for respiratory gating in cardiac PET imaging

Respiratory gating is a common technique used to compensate for patient breathing motion and decrease the prevalence of image artifacts that can impact diagnoses. In this study a new data-driven respiratory gating method (PeTrack) was compared with a conventional optical tracking system. The performance of respiratory gating of the two systems was evaluated by comparing the number of respiratory triggers, patient breathing intervals and gross heart motion as measured in the respiratory-gated image reconstructions of rubidium-82 cardiac PET scans in test and control groups consisting of 15 and 8 scans, respectively. We found evidence suggesting that PeTrack is a robust patient motion tracking system that can be used to retrospectively assess patient motion in the event of failure of the conventional optical tracking system