Gated Positron Emission Tomography Images Research Articles

PET-determined myocardial perfusion and flow in coronary artery disease characterization

Positron emission tomography (PET) myocardial perfusion imaging in conjunction with tracer-kinetic modeling enables the concurrent assessment of myocardial perfusion and regional myocardial blood flow (MBF) of the left ventricle in absolute terms in milliliters per gram per minute (mL/g/min). The non-invasive quantification of MBF during pharmacologically induced hyperemia, at rest, and corresponding myocardial flow reserve (MFR) opens a new avenue for the identification and characterization of classical or endogen type of coronary microvascular dysfunction (CMD) as functional substrate for microvascular angina in patients with non-obstructive coronary artery disease (CAD) and/or no CAD at all. Further, PET-MBF quantification expands the scope of conventional myocardial perfusion imaging from the identification of advanced, and flow-limiting, epicardial CAD to early stages of atherosclerosis and/or CMD. Adding MBF assessment to myocardial perfusion may also reliably unravel diffuse ischemia owing to significant left main stenosis and/or multivessel CAD, confirmed by peak stress transient ischemic cavity dilation of the left ventricle during maximal vasomotor stress on gated PET images. Owing to high spatial and contrast resolution in conjunction with photon-attenuation free myocardial perfusion PET images, PET is preferentially used for CAD in advanced obesity and women with pronounced breast habitus. With increasing clinical use of cardiac PET perfusion and MBF assessment, individualized, and image-guided cardiovascular treatment decisions in CAD patients is likely to ensue, while its translation into improved cardiovascular outcome remains to be investigated.

Higher-order singular value decomposition-based lung parcellation for breathing motion management.

Positron emission tomography (PET) imaging of the lungs is confounded by respiratory motion-induced blurring artifacts that degrade quantitative accuracy. Gating and motion-compensated image reconstruction are frequently used to correct these motion artifacts in PET. In the absence of voxel-by-voxel deformation measures, surrogate signals from external markers are used to track internal motion and generate gated PET images. The objective of our work is to develop a group-level parcellation framework for the lungs to guide the placement of markers depending on the location of the internal target region. We present a data-driven framework based on higher-order singular value decomposition (HOSVD) of deformation tensors that enables identification of synchronous areas inside the torso and on the skin surface. Four-dimensional (4-D) magnetic resonance (MR) imaging based on a specialized radial pulse sequence with a one-dimensional slice-projection navigator was used for motion capture under free-breathing conditions. The deformation tensors were computed by nonrigidly registering the gated MR images. Group-level motion signatures obtained via HOSVD were used to cluster the voxels both inside the volume and on the surface. To characterize the parcellation result, we computed correlation measures across the different regions of interest (ROIs). To assess the robustness of the parcellation technique, leave-one-out cross-validation was performed over the subject cohort, and the dependence of the result on varying numbers of gates and singular value thresholds was examined. Overall, the parcellation results were largely consistent across these test cases with Jaccard indices reflecting high degrees of overlap. Finally, a PET simulation study was performed which showed that, depending on the location of the lesion, the selection of a synchronous ROI may lead to noticeable gains in the recovery coefficient. Accurate quantitative interpretation of PET images is important for lung cancer management. Therefore, a guided motion monitoring approach is of utmost importance in the context of pulmonary PET imaging.

The clinical utility of phase-based respiratory gated PET imaging based on visual feedback with a head-mounted display system

We developed a new respiratory-gated positron emission tomography (PET) imaging method (RGV-PET) that phase-based respiratory gated PET imaging (RG-PET) combine with head-mounted display (HMD)-guided "visual feedback." The purpose of this study was to investigate whether RGV-PET is effective at improving the quantitative measurement of tracer uptake in tumors using the phase-based respiratory gating method. Of the 41 enrolled patients with hepatobiliary or pancreatic cancer, 20 patients underwent RGV-PET and the remaining 21 patients underwent RG-PET. We measured the peak standardized uptake value (SUVpeak) of the primary lesion in each five bins obtained from both RG-PET and RGV-PET. The SUVpeak change rate calculated based on the ungated PET imaging. To evaluate the quantitative variation, the coefficient of variation of the SUVpeak change rate was compared between RG-PET and RGV-PET. In addition, we performed qualitative evaluation using visual score for the incidence of artifacts on four-dimensional-CT. The coefficient of variation of the average SUVpeak change rate in RGV-PET was 7.01 ± 4.43, which was significantly lower than the values in RG-PET (10.72 ± 5.74, p < 0.05). A significant improvement in the SUVpeak change rate of RGV-PET was obtained in bins 1 and 2 compared to RG-PET ( p < 0.05). The visual score of RGV-PET was significantly lower than RG-PET ( p < 0.05). RGV-PET was effective for respiratory stabilization and improved respiratory gating imaging quality. The RGV-PET is applicable to various PET/CT respiratory gating imaging and may improve the quantitativeness of PET images.

Correction of respiratory and cardiac motion in cardiac PET/MR using MR-based motion modeling

Cardiac positron emission tomography (PET) imaging suffers from image blurring due to the constant motion of the heart that can impact interpretation. Hybrid PET/magnetic resonance (MR) has the potential to use radiation-free MR imaging to correct for the effects of cardio-respiratory motion in the PET data, improving qualitative and quantitative PET imaging in the heart. The purpose of this study was (i) to implement a MR image-based motion-corrected PET/MR method and (ii) to perform a proof-of-concept study of quantitative myocardial PET data in patients.The proposed method takes reconstructions of respiratory and cardiac gated PET data and applies spatial transformations to a single reference frame before averaging to form a single motion-corrected PET (MC-PET) image. Motion vector fields (MVFs) describing the transformations were derived from affine or non-rigid registration of respiratory and cardiac gated MR data.Eight patients with suspected cardiac sarcoidosis underwent cardiac PET/MR imaging after injection of 5 MBq kg−1 of 18F-fluorodeoxyglucose (18F-FDG). Myocardial regions affected by motion were identified by expert readers within which target-to-background ratios (TBR) and contrast-to-noise ratios (CNR) were measured on non-MC-non-gated, MC-PET, and double respiratory and cardiac gated PET images. Paired t-tests were used to determine statistical differences in quantitative uptake-measures between the different types of PET images.MC-PET images showed less blurring compared to non-MC-non-gated PET and tracer activity qualitatively aligned better with the underlying myocardial anatomy when fused with MR. TBR and CNR were significantly greater for MC-PET (2.8 ± 0.9; 21 ± 22) compared to non-MC-non-gated PET (2.4 ± 0.9, p = 0.0001; 15 ± 13, p = 0.02), while TBR was lower and CNR greater compared to double-gated PET (3.2 ± 0.9, p = 0.04; 6 ± 3, p = 0.004).This study demonstrated in a patient cohort that motion-corrected (MC) cardiac PET/MR is feasible using a retrospective MR image-based method and that improvement in TBR and CNR are achievable. MC PET/MR holds promise for improving interpretation and quantification in cardiac PET imaging.

An image reconstruction method with a locally adaptive gating scheme for PET data

In conventional gating approaches for positron emission tomography (PET), a single number of gates is predetermined for the whole field of view (FOV) regardless of spatially variant motion blurring effects, which compromises image quality by under-gating regions of large motion and over-gating static regions. To achieve the best resolution–noise trade-off for the whole FOV, we proposed a new approach that incorporates a spatially variant number of gates into gated image reconstruction. The first step was to estimate the motion amplitude of each spatial location. A preliminary set of gated image reconstructions was generated from the PET data. The spatially variant motion amplitudes were approximated based on the registration of 2D maximum intensity projections of the gated reconstructions as well as prior knowledge. Second, the spatially varying motion amplitudes were used to determine the optimal number of gates for each region. Finally, the adaptive gating image reconstruction algorithm that incorporates a gating transform function to model the spatially variant number of gates was applied to generate adaptively gated 4D images. Scans from large FOV systems were simulated using actual multi-bed patient data from a clinical scanner for evaluation purposes. Images reconstructed with the conventional gating scheme as well as static reconstruction were obtained for comparison with the results obtained using our new method. In areas with lower estimated motion amplitudes (such as the spine), the reconstructed images using the new approach showed reduced noise compared to images with conventional gated reconstructions and comparable quality with non-gated images. In areas with large estimated motion amplitudes, such as in the lung and liver, contrast and resolution of images using the new method and conventional gated-reconstructions were comparable, and both were higher than those of non-gated images. The results indicate that using a locally adaptive number of gates based on respiratory motion amplitude instead of a fixed number of gates can improve the statistics of gated PET images by optimizing the local noise–resolution trade-off.

A novel dual gating approach using joint inertial sensors: implications for cardiac PET imaging

Positron emission tomography (PET) is a non-invasive imaging technique which may be considered as the state of art for the examination of cardiac inflammation due to atherosclerosis. A fundamental limitation of PET is that cardiac and respiratory motions reduce the quality of the achieved images. Current approaches for motion compensation involve gating the PET data based on the timing of quiescent periods of cardiac and respiratory cycles. In this study, we present a novel gating method called microelectromechanical (MEMS) dual gating which relies on joint non-electrical sensors, i.e. tri-axial accelerometer and gyroscope. This approach can be used for optimized selection of quiescent phases of cardiac and respiratory cycles. Cardiomechanical activity according to echocardiography observations was investigated to confirm whether this dual sensor solution can provide accurate trigger timings for cardiac gating. Additionally, longitudinal chest motions originating from breathing were measured by accelerometric- and gyroscopic-derived respiratory (ADR and GDR) tracking. The ADR and GDR signals were evaluated against Varian real-time position management (RPM) signals in terms of amplitude and phase. Accordingly, high linear correlation and agreement were achieved between the reference electrocardiography, RPM, and measured MEMS signals. We also performed a Ge-68 phantom study to evaluate possible metal artifacts caused by the integrated read-out electronics including mechanical sensors and semiconductors. The reconstructed phantom images did not reveal any image artifacts. Thus, it was concluded that MEMS-driven dual gating can be used in PET studies without an effect on the quantitative or visual accuracy of the PET images. Finally, the applicability of MEMS dual gating for cardiac PET imaging was investigated with two atherosclerosis patients. Dual gated PET images were successfully reconstructed using only MEMS signals and both qualitative and quantitative assessments revealed encouraging results that warrant further investigation of this method.

Maximum-Likelihood Joint Image Reconstruction/Motion Estimation in Attenuation-Corrected Respiratory Gated PET/CT Using a Single Attenuation Map.

This work provides an insight into positron emission tomography (PET) joint image reconstruction/motion estimation (JRM) by maximization of the likelihood, where the probabilistic model accounts for warped attenuation. Our analysis shows that maximum-likelihood (ML) JRM returns the same reconstructed gates for any attenuation map (μ-map) that is a deformation of a given μ-map, regardless of its alignment with the PET gates. We derived a joint optimization algorithm accordingly, and applied it to simulated and patient gated PET data. We first evaluated the proposed algorithm on simulations of respiratory gated PET/CT data based on the XCAT phantom. Our results show that independently of which μ-map is used as input to JRM: (i) the warped μ-maps correspond to the gated μ-maps, (ii) JRM outperforms the traditional post-registration reconstruction and consolidation (PRRC) for hot lesion quantification and (iii) reconstructed gated PET images are similar to those obtained with gated μ-maps. This suggests that a breath-held μ-map can be used. We then applied JRM on patient data with a μ-map derived from a breath-held high resolution CT (HRCT), and compared the results with PRRC, where each reconstructed PET image was obtained with a corresponding cine-CT gated μ-map. Results show that JRM with breath-held HRCT achieves similar reconstruction to that using PRRC with cine-CT. This suggests a practical low-dose solution for implementation of motion-corrected respiratory gated PET/CT.

Assessment of patient selection criteria for quantitative imaging with respiratory-gated positron emission tomography.

The objective of this investigation was to propose techniques for determining which patients are likely to benefit from quantitative respiratory-gated imaging by correlating respiratory patterns to changes in positron emission tomography (PET) metrics. Twenty-six lung and liver cancer patients underwent PET/computed tomography exams with recorded chest/abdominal displacements. Static and adaptive amplitude-gated [[Formula: see text]]fluoro-D-glucose (FDG) PET images were generated from list-mode acquisitions. Patients were grouped by respiratory pattern, lesion location, or degree of lesion attachment to anatomical structures. Respiratory pattern metrics were calculated during time intervals corresponding to PET field of views over lesions of interest. FDG PET images were quantified by lesion maximum standardized uptake value ([Formula: see text]). Relative changes in [Formula: see text] between static and gated PET images were tested for association to respiratory pattern metrics. Lower lung lesions and liver lesions had significantly higher changes in [Formula: see text] than upper lung lesions (14 versus 3%, [Formula: see text]). Correlation was highest ([Formula: see text], [Formula: see text], [Formula: see text]) between changes in [Formula: see text] and nonstandard respiratory pattern metrics. Lesion location had a significant impact on changes in PET quantification due to respiratory gating. Respiratory pattern metrics were correlated to changes in [Formula: see text], though sample size limited statistical power. Validation in larger cohorts may enable selection of patients prior to acquisition who would benefit from respiratory-gated PET imaging.

TH-A-WAB-09: The Potential of Positron Emission Tomography (PET) for Intra-Treatment Dynamic Tumor Tracking During Radiotherapy: A Phantom Study

Purpose: This study aimed to evaluate the potential and feasibility of positron emission tomography (PET) for dynamic tumor tracking during radiation treatment. We have proposed a center of mass (CoM) tumor tracking algorithm and investigated the geometric accuracy of the algorithm. Methods: The proposed PET dynamic tumor tracking algorithm estimated the target position information through the CoM of the segmented target volume on gated PET images which were continuously updated throughout a scan. External respiratory motion and list‐mode PET data were acquired from a phantom programmed to move with measured respiratory traces. The phantom was cylindrical with six sphere targets (10, 13, 17, 22, 28, and 37 mm in diameter). To test the algorithm on respiratory motion with clinical variability, respiratory traces of higher than average magnitudes and complexity were selected from a large database. The traces were 3D‐measured motion representing typical motion (T1), baseline variations (T2), predominantly left‐right motion (T3), and high‐frequency breathing (T4). Estimation errors were quantified through Euclidean distances between the motion traces and estimated CoM trajectories. Results: The overall time‐averaged error was 1.6 mm over all traces (T1‐T4) of all targets. There were small variations in the errors between the traces, although they were very distinct. The overall time‐averaged error of each trace (T1‐T4) was 1.3, 1.3, 1.7, and 2.2 mm, respectively. The accuracy of the estimates was consistent for all targets except the smallest one: For the 17 mm target, the overall time‐averaged errors of T1‐T4 were 1.2, 1.2, 1.4, and 1.7 mm, respectively; For the 10 mm target, those of T1‐T4 were 2.3, 2.2, 2.6, and 3.9 mm, respectively. Conclusion: We developed an algorithm using list‐mode PET data and external respiratory motion data for dynamic tumor tracking in a combined PET‐linac system. The overall tracking error in phantom studies was less than 2 mm. Research supported by the Kwanjeong Educational Foundation, NIH/NCI R01 93626, Stanford Bio‐X, NHMRC Australia Fellowship, NIH/NCI through SBIR with RefleXion Medical R43CA153466.

Paradoxical septal motion from prior coronary artery bypass graft surgery does not impact left ventricular mechanical dyssynchrony by gated myocardial perfusion imaging

BackgroundPhase analysis of gated myocardial perfusion imaging (MPI) provides automated and reproducible assessment of left ventricular (LV) mechanical dyssynchrony (LVMD) (phase standard deviation [SD]). Many patients undergoing gated MPI have history of prior coronary artery bypass graft surgery (CABG). The latter is often associated with paradoxical septal wall motion (PSM). The effect of prior CABG and PSM on LVMD has not been evaluated. Methods and ResultsFrom the single-photon emission computed tomography (SPECT) and positron emission tomography (PET) MPI clinical database maintained at the Cleveland Clinic, we identified 200 consecutive patients with SPECT (100 control with normal LV ejection fraction [EF], MPI, and QRS < 120 ms; and 100 with LVEF < 35%), and 631 patients with LVEF < 35% with gated PET. Patients with QRS ≥ 120 ms, bundle branch block, ventricular pacing or isolated non-CABG surgery were excluded. There were 162 patients with gated SPECT (46 with prior CABG), and 568 with gated PET (220 with prior CABG) that were left for analysis. Phase SD was derived using Emory Cardiac Toolbox (ECTb) (for gated SPECT) and Corridor 4DM (4DM) (for gated SPECT and PET images). Multivariate linear regression analysis was performed to assess whether prior CABG was an independent predictor of worse LV mechanical dyssynchrony. After adjusting for patients’ demographics, co-morbidities, medications, and MPI data, history of prior CABG was not and independent predictor of LV mechanical dyssynchrony (P = .67 with 4DM, P = .97 with ECTb) in patients undergoing gated SPECT or among patients undergoing gated PET imaging (P = .18). ConclusionsAlthough paradoxical septal wall motion is commonly seen after cardiac surgery, prior CABG does not affect or impact LV mechanical dyssynchrony indices measured from gated SPECT or PET images. Whether dyssynchrony measurements with echocardiography that has higher temporal resolution might uncover intraventricular delays, remains to be determined.

Effect of stress testing on left ventricular mechanical synchrony by phase analysis of gated positron emission tomography in patients with normal myocardial perfusion

There are limited data on whether differences exist in left ventricular (LV) mechanical dyssynchrony indices derived from stress versus rest gated positron emission tomography (PET) in patients with normal myocardial perfusion imaging (MPI). Stress/rest (82)Rb gated PET was performed in consecutive patients with normal MPI between 2006 and 2010. Patients were divided into two groups: group 1 [LV ejection fraction (EF) ≥ 55% and QRS < 120 ms] and group 2 (LVEF ≤35%). Images were acquired on a dedicated PET scanner prior to and on a hybrid PET/CT system after November 2008. LV dyssynchrony indices [phase standard deviation (SD)° and SD (ms)] were derived from stress and rest gated images. There were 91 patients in group 1 (age 61 ± 13, LVEF 66 ± 8%, normal QRS) and 126 in group 2 (age 66 ± 12, LVEF 25 ± 7%). The stress derived LVEF were significantly higher than rest for either group (p < 0.0001). Patients with cardiomyopathy had significantly higher dyssynchrony indices compared to those with normal LVEF (rest SD° 49.2 ± 21.5° vs 16.8 ± 7.8° and stress SD° 42.5 ± 19.4° vs 12.4 ± 3.7°, respectively, p < 0.0001 for both). The dyssynchrony indices derived from rest gated images were significantly higher than those derived from stress in both groups (p < 0.001 by unpaired and paired t test) and irrespective of the type of PET scanner utilized. Finally, 20/87 (23%) patients with normal LVEF and 27/66 (41%) of those with cardiomyopathy but without dyssynchrony based on stress indices were recategorized as having significant dyssynchrony given their resting indices. LV mechanical dyssynchrony indices by phase analysis are smaller when derived from peak stress versus rest gated PET imaging in patients with normal MPI, irrespective of the resting LVEF.

Super-Resolution in Respiratory Synchronized Positron Emission Tomography

Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times.

Generating lung tumor internal target volumes from 4D-PET maximum intensity projections

Positron emission tomography (PET) of lung tumors suffers from breathing-motion induced blurring. Respiratory-correlated PET ameliorates motion blurring and enables visualization of lung tumor functional uptake throughout the breathing cycle but has achieved limited clinical use in radiotherapy planning. In this work, the authors propose a process for generating a gated PET maximum intensity projection (MIP), a breathing-phase projection of the 4D image set comprising gated PET images, as a technique to quantitatively and efficiently incorporate respiratory-correlated PET information into radiotherapy treatment planning. 4D-CT and respiratory-gated PET using [(18)F]fluorodeoxyglucose (FDG) were acquired of three patients with a total of four small (4-18 cc), clearly defined lower-lobe lung tumors. Internal target volumes (ITVs) for the lung tumors were generated by threshold-based segmentation of PET-MIP images and ungated PET images (ITV(PET-MIP) and ITV(3D-PET), respectively), and by manual contouring of CT-MIP and end-exhale and end-inhale phases of 4D-CT (ITV(CT-MIP)) by a radiation oncologist. Because of the sensitivity of tumor segmentation to threshold value, several different thresholds were tested for ITV generation, including 40%, 30%, and 20% of maximum standardized uptake value (SUV(max)) for FDG as well as absolute SUV thresholds of 2.5 and 3.0. The normalized overlap and relative volumes of ITV(PET-MIP) and ITV(3D-PET) with respect to ITV(CT-MIP) were compared. The images were also visually compared. ITV(CT-MIP) was considered a gold standard for these tumors with CT-visible morphology. The mean and standard deviation normalized overlap and relative volumes between ITV(PET-MIP) and ITV(CT-MIP) were 0.68 ± 0.07 and 1.07 ± 0.42, respectively, averaged over all four tumors and all five threshold values. The mean and standard deviation normalized overlap and relative volumes of ITV(3D-PET) and ITV(CT-MIP) were 0.47 ± 0.12 and 0.69 ± 0.56, respectively. PET-MIP images better match CT-MIP images for this sample of four small CT-visible tumors as compared to ungated PET images, based on the metrics of volumetric overlap and relative volumes as well as visual interpretation. The PET-MIP is a way to incorporate 4D-PET imaging into the process of lung tumor contouring that is time-efficient for the radiation oncologist and involves minimal effort to implement in treatment planning software, because it requires only a single PET image beyond contouring on CT alone.

SU‐E‐T‐285: Generating Lung Tumor Internal Target Volumes from 4D‐PET Maximum Intensity Projections

Purpose: Positron emission tomography (PET) of lung tumors suffers from breathing‐motion induced blurring. Gated PET ameliorates motion blurring and enables visualization of lung tumor functional uptake throughout the breathing cycle but has achieved limited clinical use in radiotherapy planning. We propose a process for generating a gated PET maximum intensity projection (MIP), a 3D projection of the 4D image set comprising gated PET images, as a technique to efficiently and quantitatively incorporate respiratory‐correlated PET information into radiotherapy treatment planning. Methods: 4DCT and respiratory‐gated FDG‐PET list‐mode data were acquired of 3 patients with a total of 4 small (4–18cc), well‐encapsulated lower‐lobe lung tumors. Internal target volumes (ITVs) for the lung tumors were generated by threshold‐based segmentation of the PET‐MIP images and the un‐gated PET images, and by manual contouring of the tumor in a 4DCT‐MIP image. The normalized overlap volumes and relative volumes of ITV&lt;sub&gt;PET‐MIP&lt;/sub&gt; and ITV&lt;sub&gt;UNGATED‐PET&lt;/sub&gt; with respect to ITV&lt;sub&gt;CT‐MIP&lt;/sub&gt; were compared. The images were also visually compared. ITV&lt;sub&gt;CT‐MIP&lt;/sub&gt; was considered the gold standard for these tumors having CT‐visible morphology. Results: The mean and standard deviation normalized overlap and relative volumes between ITV&lt;sub&gt;PET‐MIP&lt;/sub&gt; and ITV&lt;sub&gt;CT‐MIP&lt;/sub&gt; were 0.68+−0.07 and 1.07+−0.42, respectively, averaged over all 4 tumors and 5 segmentation‐threshold values. The mean and standard deviation normalized overlap and relative volumes of ITV&lt;sub&gt;UNGATED‐PET&lt;/sub&gt; and ITV&lt;sub&gt;CT‐MIP&lt;/sub&gt; were 0.47+−0.12 and 0.69+−0.56 respectively. Conclusions: PET‐MIP images better match CT‐MIP images for this sample of four small CT‐visible tumors, as compared to un‐gated PET images, based on the metrics of volumetric overlap and relative volumes as well as on visual interpretation. The PET‐MIP is a way to incorporate 4DPET imaging into the process of lung tumor contouring that is time‐efficient for the radiation oncologist and involves minimal effort to implement in treatment planning software because it requires only a single PET image beyond CT‐alone contouring.

TU‐E‐BRC‐04: High‐Statistics Breathing Motion‐Corrected Positron Emission Tomography by Deforming and Stacking Gated PET Images Using 4DCT‐Derived Motion Vectors

Purpose: Positron emission tomography (PET) of lung tumors suffers due to breathing‐motion induced blurring. Gated PET ameliorates motion blurring, but the concomitant reduction in coincidence‐event statistics per gated image leads to increased image noise, decreasing the utility of the images. In this work we demonstrate a method of reducing motion‐induced blurring from PET images without decreasing coincidence‐event statistics. Methods: The method works by deforming and stacking gated PET images using lung tissue motion vectors derived from deformable image registration performed between the phases of respiratory‐correlated computed tomography (4DCT) images. A duration of 12 minutes of respiratory‐correlated FDG‐PET data in list‐mode format and two 4DCT scans were acquired from 3 patients with a total of 4 small (4–18cc) lung tumors. A motion‐corrected image was produced using the first 2 minutes of list‐mode data. The motion‐corrected image was compared to a high‐statistics gated end‐exhale PET image created from the remaining 10 minutes of PET list‐mode data, which was used as a gold‐standard approximating a truly motion‐free image. The images were also compared against an un‐gated PET image produced using the first two minutes of list‐mode data, to quantify the improvement provided by the motion‐correction process. Results: Tumor SUVmax was on average 44% higher for motion‐reduced images relative to un‐gated images, but still on average 14% lower than the gold‐standard high‐statistics gated images. Volumes of tumors segmented at 40% of SUVmax were on average 32% lower relative to un‐gated images, but still 22% higher than the high‐statistics gated images. Conclusions: A process for reducing motion blurring in PET images without increasing image noise was demonstrated. The motion‐corrected images are quantitatively and qualitatively improved relative to un‐gated images, however further improvement is needed in order to match the quality of high‐statistics gated images.

SU‐C‐110‐03: Utility of Maximum Intensity Projections of Gated PET Images in Determining Internal Target Volumes of Moving Lung Tumors: A Phantom Study

Purpose: To examine maximum intensity projections (MIPs) as a method for segmenting lung tumor internal target volumes (ITVs) in positron emission tomography (PET) images using two threshold‐based methods, and to assess various parameters that potentially affect the accuracy of tumor segmentation by this technique. Methods and Materials: An acrylic phantom setup, consisting of a 1.5cm diameter sphere filled with 11 ‐C solution inside a cylindrical bath of 18‐fluorodeoxyglucose solution, was used for a PET list‐mode acquisition. The phantom was attached to a robotic arm that moved according to four patient breathing trajectories via an abdominal breathing bellows device. List‐mode data was gated based on the breathing trajectories, and PET‐MIPs were created from the reconstructed gated images. ITVs were calculated and compared for both un‐gated PET images and PET‐MIPs by using varying thresholds of absolute standardized uptake value (SUV) and percentage of maximum SUV. In addition, a simulation of PET‐MIPs was performed to examine the effects of tumor size, image smoothing, and tumor trajectory on the accuracy of ITV measurement. Results: For any given threshold value, PET‐MIPs tended to produce larger ITVs than un‐gated PET. For optimal percentage thresholds across all trajectories, PET‐MIPs measured an ITV to within 5% accuracy in a larger SUV range with lower initial values than un‐gated PET for the same accuracy. For both PET‐MIP and un‐gated PET, a percentage threshold method produced a smaller deviation from true ITV in similar SUV ranges when compared to an absolute threshold method. The PET‐MIP simulation demonstrated greater accuracy of ITV measurement with increased image smoothing and sphere size. Breathing trajectories exhibiting baseline drift negatively impacted accurate ITV determination. Conclusion: Threshold‐based ITV segmentation is sensitive to lung tumor volume, trajectory, and SUV. PET‐MIPs appear to be a promising tool in the accurate delineation of lung tumor ITV.

Analytical-Based Partial Volume Recovery in Mouse Heart Imaging

Positron emission tomography (PET) is a powerful imaging modality that has the ability to yield quantitative images of tracer activity. Physical phenomena such as photon scatter, photon attenuation, random coincidences and spatial resolution limit quantification potential and must be corrected to preserve the accuracy of reconstructed images. This study focuses on correcting the partial volume effects that arise in mouse heart imaging when resolution is insufficient to resolve the true tracer distribution in the myocardium. The correction algorithm is based on fitting 1D profiles through the myocardium in gated PET images to derive myocardial contours along with blood, background and myocardial activity. This information is interpolated onto a 2D grid and convolved with the tomograph's point spread function to derive regional recovery coefficients enabling partial volume correction. The point spread function was measured by placing a line source inside a small animal PET scanner. PET simulations were created based on noise properties measured from a reconstructed PET image and on the digital MOBY phantom. The algorithm can estimate the myocardial activity to within 5% of the truth when different wall thicknesses, backgrounds and noise properties are encountered that are typical of healthy FDG mouse scans. The method also significantly improves partial volume recovery in simulated infarcted tissue. The algorithm offers a practical solution to the partial volume problem without the need for co-registered anatomic images and offers a basis for improved quantitative 3D heart imaging.

Motion Correction and Attenuation Correction for Respiratory Gated PET Images

Positron emission tomography (PET) is a molecular imaging technique which provides important functional information about the human body. However, thoracic PET images are often substantially degraded by respiratory motion, which adversely impacts on subsequent diagnosis. In this paper, a motion correction and attenuation correction method is proposed to correct for motion in respiratory gated PET images and to yield an accurate distribution of the radioactivity concentration. Experimental results show that this method can effectively correct for motion and improve PET image quality. The method is able to provide improved diagnostic information without increasing the acquisition time or the radiation burden.

Image-Derived Input Function from Cardiac Gated Maximum a Posteriori Reconstructed PET Images in Mice

The purpose of this study was to determine if accurate image-derived input functions (IDIF) can be measured from cardiac gated positron emission tomography (PET) images reconstructed using ordered subset expectation maximization-maximum a posteriori (OSEM-MAP) without further correction. IDIFs from the left ventricle were measured from cardiac gated PET images reconstructed using OSEM-MAP with computed tomography (CT)-based attenuation correction for five C57/BL6 mice. The accuracy of the IDIF was tested against blood samples using Bland-Altman analysis. Image-derived blood radioactivity concentration values were not significantly different from sampled blood values at two late time points as determined by a paired t test (P = 0.97). Bland-Altman analysis revealed a mean difference of 0.06 μCi/ml (1%). Using kinetic analysis, the mean myocardial 2-deoxy-2-[(18)F]fluoro-D-glucose uptake rate constant based on the IDIF was comparable to values reported in the literature based on physical blood sampling. Accurate IDIFs can be obtained non-invasively. Although reconstruction times are increased, no further spillover corrections are necessary for IDIFs derived from gated, OSEM-MAP reconstructed images with attenuation correction.

A simple respiration gating technique and its application in high-resolution PET camera

We have developed a simple technique to gate positron emission tomography (PET) imaging in synchronization with respiratory motion to reduce image blurring caused by breathing and improve quantification of tracer uptake in lesions in the chest and abdomen, especially in very high-resolution PET systems. Taking advantage of the temperature differences in the air flow in a nostril due to inhalations and exhalations, a simple solid thermometer was used to construct a respiratory gating system to monitor the respiratory cycles. The gating system provided trigger signals synchronous with respiration and 40 Hz timing marks. These trigger signals and timing marks were inserted into the data stream in real-time while the PET camera was taking data. The gating trigger signals represent a particular phase of respiratory motion, and the evenly cycled timing marks were designed for motion-image frame registration. This gating system was implemented and tested with our MDAPET, a very high-resolution (2.7-mm resolution) PET camera developed at The University of Texas M. D. Anderson Cancer Center. A volunteer with 2 spherical lesion phantoms (diameters 3 mm and 5 mm) placed on the abdomen close to the navel was scanned in the gated mode. The respiration-gated images of the lesion phantoms were compared and studied. The simple respiratory gating system worked well in terms of detecting the breathing cycle and providing gating trigger signals and timing marks. Image blur and errors in the measurements of the lesions' volumes in the gated PET images were reduced, compared with those of the non-gated PET images.