The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Klaus P. Schäfers - One of the best experts on this subject based on the ideXlab platform.

  • a mass conservation based optical flow method for Cardiac motion correction in 3d PET
    Medical Physics, 2013
    Co-Authors: Mohammad Dawood, Fabian Gigengack, Xiaoyi Jiang, Klaus P. Schäfers
    Abstract:

    Purpose: Cardiac positron emission tomography (PET) images usually show two kinds of artifacts: the limited resolution of PET leads to partial volume effects and the motion of the heart induces blurring. These phenomena degrade the PET images and induce errors in the quantification. One method of reducing this problem is to use gated PET data. However, the reduction of information per phase leads to an increase in noise on the reconstructed images. Alternatively, the PET data have to be corrected for motion and partial volume effects. Methods: Optical flow methods have been shown to accurately estimate the motion between PET image frames. These methods assume that the brightness of the objects remains constant between the frames. This condition is not fulfilled in Cardiac PET data because the brightness of the Cardiac muscle tissue (myocardium) is not accurately resolved due to the partial volume effect. Therefore, the use of a newly developed optical flow method based upon the conservation of mass condition is proposed to correct the Cardiac PET data. Mass conservation is applicable to PET images as the total activity in the field of view may be assumed to remain almost constant, if the data are precorrected for radioactive decay. Two variants of the method using the quadratic and the nonquadratic penalization are presented. The methods were evaluated with respect to correlation coefficient, myocardial thickness and the blood pool activity in the left ventricle on phantom data and on 14 patient image volumes. Results: The proposed methods showed that the Cardiac motion can be efficiently corrected despite partial volume effects. The correlation coefficient between the image volumes increased from 0.87 to 0.98 on average. The change in myocardial thickness was reduced from 28% to 3%. The variation in blood pool activity was reduced from 80% to 8%. The algorithm needed only about 4 s for execution. Conclusions: A mass preserving optical flow method of Cardiac motion correction in 3D PET data has been presented and tested on phantom as well as patient data. The results show that the motion was corrected for all datasets effectively.

  • motion correction in dual gated Cardiac PET using mass preserving image registration
    IEEE Transactions on Medical Imaging, 2012
    Co-Authors: Fabian Gigengack, Lars Ruthotto, Martin Burger, Carsten H Wolters, Xiaoyi Jiang, Klaus P. Schäfers
    Abstract:

    Respiratory and Cardiac motion leads to image degradation in positron emission tomography (PET) studies of the human heart. In this paper we present a novel approach to motion correction based on dual gating and mass-preserving hyperelastic image registration. Thereby, we account for intensity modulations caused by the highly nonrigid Cardiac motion. This leads to accurate and realistic motion estimates which are quantitatively validated on software phantom data and carried over to clinically relevant data using a hardware phantom. For patient data, the proposed method is first evaluated in a high statistic (20 min scans) dual gating study of 21 patients. It is shown that the proposed approach properly corrects PET images for dual-Cardiac as well as respiratory-motion. In a second study the list mode data of the same patients is cropped to a scan time reasonable for clinical practice (3 min). This low statistic study not only shows the clinical applicability of our method but also demonstrates its robustness against noise obtained by hyperelastic regularization.

  • detection of respiratory tumour motion using intrinsic list mode driven gating in positron emission tomography
    European Journal of Nuclear Medicine and Molecular Imaging, 2010
    Co-Authors: Florian Buther, Iris Ernst, Mohammad Dawood, Peter Kraxner, Michael Schafers, Otmar Schober, Klaus P. Schäfers
    Abstract:

    Purpose Respiratory motion of organs during PET scans is known to degrade PET image quality, potentially resulting in blurred images, attenuation artefacts and erroneous tracer quantification. List mode-based gating has been shown to reduce these pitfalls in Cardiac PET. This study evaluates these intrinsic gating methods for tumour PET scans.

  • respiratory gating of Cardiac PET data in list mode acquisition
    European Journal of Nuclear Medicine and Molecular Imaging, 2006
    Co-Authors: Lefteris Livieratos, L. Stegger, Klaus P. Schäfers, Dale L. Bailey, Kim Rajappan, Paolo G. Camici
    Abstract:

    Respiratory motion has been identified as a source of artefacts in most medical imaging modalities. This paper reports on respiratory gating as a means to eliminate motion-related inaccuracies in PET imaging. Respiratory gating was implemented in list mode with physiological signal recorded every millisecond together with the PET data. Respiration was monitored with an inductive respiration monitor using an elasticised belt around the patient’s chest. Simultaneous ECG gating can be maintained independently by encoding ECG trigger signal into the list-mode data. Respiratory gating is performed in an off-line workstation with gating parameters defined retrospectively. The technique was applied on a preliminary set of patient data with C15O. Motion was visually observed in the cine displays of the sagittal and coronal views of the reconstructed respiratory gated images. Significant changes in the cranial–caudal position of the heart could be observed. The centroid of the Cardiac blood pool showed an excursion of 4.5–16.5 mm (mean 8.5±4.8 mm) in the cranial–caudal direction, with more limited excursion of 1.1–7.0 mm (mean 2.5±2.2 mm) in the horizontal direction and 1.3–3.7 mm (mean 2.4±0.9 mm) in the vertical direction. These preliminary data show that the extent of motion involved in respiration is comparable to myocardial wall thickness, and respiratory gating may be considered in order to reduce this effect in the reconstructed images.

  • Rigid-body transformation of list-mode projection data for respiratory motion correction in Cardiac PET
    Physics in Medicine and Biology, 2005
    Co-Authors: Lefteris Livieratos, L. Stegger, Peter Bloomfield, Klaus P. Schäfers, Dale L. Bailey, Paolo G. Camici
    Abstract:

    High-resolution Cardiac PET imaging with emphasis on quantification would benefit from eliminating the problem of respiratory movement during data acquisition. Respiratory gating on the basis of list-mode data has been employed previously as one approach to reduce motion effects. However, it results in poor count statistics with degradation of image quality. This work reports on the implementation of a technique to correct for respiratory motion in the area of the heart at no extra cost for count statistics and with the potential to maintain ECG gating, based on rigid-body transformations on list-mode data event-by-event. A motion-corrected data set is obtained by assigning, after pre-correction for detector efficiency and photon attenuation, individual lines-of-response to new detector pairs with consideration of respiratory motion. Parameters of respiratory motion are obtained from a series of gated image sets by means of image registration. Respiration is recorded simultaneously with the list-mode data using an inductive respiration monitor with an elasticized belt at chest level. The accuracy of the technique was assessed with point-source data showing a good correlation between measured and true transformations. The technique was applied on phantom data with simulated respiratory motion, showing successful recovery of tracer distribution and contrast on the motion-corrected images, and on patient data with C15O and 18FDG. Quantitative assessment of preliminary C15O patient data showed improvement in the recovery coefficient at the centre of the left ventricle.

Jinsong Ouyang - One of the best experts on this subject based on the ideXlab platform.

  • body motion detection and correction in Cardiac PET phantom and human studies
    Medical Physics, 2019
    Co-Authors: Tao Sun, Sally Ji Who Kim, Yoann Petibon, Georges El Fakhri, Paul Kyu Han, Nathaniel M Alpert, Jinsong Ouyang
    Abstract:

    Purpose Patient body motion during a Cardiac positron emission tomography (PET) scan can severely degrade image quality. We propose and evaluate a novel method to detect, estimate, and correct body motion in Cardiac PET. Methods Our method consists of three key components: motion detection, motion estimation, and motion-compensated image reconstruction. For motion detection, we first divide PET list-mode data into 1-s bins and compute the center of mass (COM) of the coincidences' distribution in each bin. We then compute the covariance matrix within a 25-s sliding window over the COM signals inside the window. The sum of the eigenvalues of the covariance matrix is used to separate the list-mode data into "static" (i.e., body motion free) and "moving" (i.e. contaminated by body motion) frames. Each moving frame is further divided into a number of evenly spaced sub-frames (referred to as "sub-moving" frames), in which motion is assumed to be negligible. For motion estimation, we first reconstruct the data in each static and sub-moving frame using a rapid back-projection technique. We then select the longest static frame as the reference frame and estimate elastic motion transformations to the reference frame from all other static and sub-moving frames using nonrigid registration. For motion-compensated image reconstruction, we reconstruct all the list-mode data into a single image volume in the reference frame by incorporating the estimated motion transformations in the PET system matrix. We evaluated the performance of our approach in both phantom and human studies. Results Visually, the motion-corrected (MC) PET images obtained using the proposed method have better quality and fewer motion artifacts than the images reconstructed without motion correction (NMC). Quantitative analysis indicates that MC yields higher myocardium to blood pool concentration ratios. MC also yields sharper myocardium than NMC. Conclusions The proposed body motion correction method improves image quality of Cardiac PET.

  • mr based Cardiac and respiratory motion correction of PET application to static and dynamic Cardiac 18 f fdg imaging
    Physics in Medicine and Biology, 2019
    Co-Authors: Yoann Petibon, Tao Sun, Paul Kyu Han, El G Fakhri, Jinsong Ouyang
    Abstract:

    Motion of the myocardium deteriorates the quality and quantitative accuracy of Cardiac PET images. We present a method for MR-based Cardiac and respiratory motion correction of Cardiac PET data and evaluate its impact on estimation of activity and kinetic parameters in human subjects. Three healthy subjects underwent simultaneous dynamic 18F-FDG PET and MRI on a hybrid PET/MR scanner. A cardiorespiratory motion field was determined for each subject using navigator, tagging and golden-angle radial MR acquisitions. Acquired coincidence events were binned into Cardiac and respiratory phases using electrocardiogram and list mode-driven signals, respectively. Dynamic PET images were reconstructed with MR-based motion correction (MC) and without motion correction (NMC). Parametric images of 18F-FDG consumption rates (Ki) were estimated using Patlak's method for both MC and NMC images. MC alleviated motion artifacts in PET images, resulting in improved spatial resolution, improved recovery of activity in the myocardium wall and reduced spillover from the myocardium to the left ventricle cavity. Significantly higher myocardium contrast-to-noise ratio and lower apparent wall thickness were obtained in MC versus NMC images. Likewise, parametric images of Ki calculated with MC data had improved spatial resolution as compared to those obtained with NMC. Consistent with an increase in reconstructed activity concentration in the frames used during kinetic analyses, MC led to the estimation of higher Ki values almost everywhere in the myocardium, with up to 18% increase (mean across subjects) in the septum as compared to NMC. This study shows that MR-based motion correction of Cardiac PET results in improved image quality that can benefit both static and dynamic studies.

  • dynamic PET imaging of myocardial glucose consumption using mr based Cardiac respiratory correction human studies
    The Journal of Nuclear Medicine, 2019
    Co-Authors: Tao Sun, Yoann Petibon, Jinsong Ouyang, Paul Kyu Han, Georges El Fakhri
    Abstract:

    177 Purpose: Motion associated respiration and Cardiac function is a well-known source of image quality degradation in Cardiac Positron Emission Tomography (PET) studies. The continuous movement of the myocardium in PET scanning introduces artifacts that alter quantification of tracer concentration in Cardiac tissues and deteriorate diagnostic quality of image. In addition to its recognized potential in clinical cardiovascular imaging a unique feature of hybrid PET/MR is its ability of providing a robust solution to the problem of motion in PET. The aim of this study was to assess the impact of MR-based Cardiac/respiratory motion correction in dynamic Cardiac PET. Methods: The motion correction method comprises of four key components: (i) Surrogate signals for the Cardiac and respiratory cycles that are acquired continuously during the dynamic PET scan and used to assign a cardiorespiratory phase index to each measured coincidence event. (ii) A deforming MR-based cardiorespiratory tissue motion model that assigns a given cardiorespiratory motion phase index to a specific 3-D motion vector field. The motion model is obtained by means of navigators, tagging and golden-angle-based radial MR acquisitions. (iii) A motion-dependent attenuation model which is generated by deforming the acquired attenuation map with the motion model. (iv) A motion-compensated PET reconstruction algorithm that incorporates the motion and attenuation models to produce a motion corrected image volume for each dynamic frame without loss of SNR. Human studies were performed to evaluate the proposed correction method. All scans were acquired on a whole-body PET-MR system (Siemens Biograph mMR). Three volunteers were recruited for the study. FDG (average radioactivity: 10 mCi) was administered intravenously and a 50-min acquisition in list mode was initiated. Dynamic PET and motion tracking MRI data were simultaneously acquired during free-breathing. Four venous blood samples were drawn at 30, 35, 40 and 45 min after tracer administration for deriving the plasma input function. The PET data for each dynamic frame were reconstructed in two ways: with the proposed MR-based motion correction (MC) method and without motion correction (NMC). Improvement in Cardiac PET image quality was assessed by quantifying the thickness of the myocardium wall as well as the myocardium contrast-to-noise ratio in a late dynamic frame. The Patlak analysis method was applied to both MC and NMC image sets to calculate voxel-wise FDG uptake rate constants (Ki) in the myocardium. Results: Fig.1a shows that for subject 1, MC images depict overall higher activity concentration, and improved resolution compared to NMC images, as evidenced by sharper myocardium wall and improved delineation of papillary muscles. Fig.1b shows box plots that quantitatively analyze the effect of motion correction on activity estimation in different regions of the myocardium. For all three subjects, the impact of MC was most significant in septum regions, where myocardium contrast-to-noise ratio increased up to 22% and wall thickness decreased up to 18% compared to the NMC images. Fig.2a shows that for subject 1, MC yielded Ki images with higher resolution and higher Ki values in the myocardium. Fig2b shows box plots that quantitatively analyze the Ki for three subjects, which increased up to 17% after MC. Conclusions: MR-based Cardiac and respiratory motion correction benefits static and dynamic FDG PET human scans. Analyses of static data indicate that motion correction produces images with higher myocardium activity concentration, lower wall thickness and improved resolution. For dynamic imaging, higher FDG consumption rates were found in the myocardium after MC for all frames. The method potentially can provide high quality images for many Cardiac PET imaging applications. This work is under support of NIH funding R01HL118261.

  • mr based motion correction for Cardiac PET parametric imaging a simulation study
    EJNMMI Physics, 2018
    Co-Authors: Yoann Petibon, Georges El Fakhri, Kui Ying, Jinsong Ouyang
    Abstract:

    Both Cardiac and respiratory motions bias the kinetic parameters measured by dynamic PET. The aim of this study was to perform a realistic positron emission tomography-magnetic resonance (PET-MR) simulation study using 4D XCAT to evaluate the impact of MR-based motion correction on the estimation of PET myocardial kinetic parameters using PET-MR. Dynamic activity distributions were obtained based on a one-tissue compartment model with realistic kinetic parameters and an arterial input function. Realistic proton density/T1/T2 values were also defined for the MRI simulation. Two types of motion patterns, Cardiac motion only (CM) and both Cardiac and respiratory motions (CRM), were generated. PET sinograms were obtained by the projection of the activity distributions. PET image for each time frame was obtained using static (ST), gated (GA), non-motion-corrected (NMC), and motion-corrected (MC) methods. Voxel-wise unweighted least squares fitting of the dynamic PET data was then performed to obtain K1 values for each study. For each study, the mean and standard deviation of K1 values were computed for four regions of interest in the myocardium across 25 noise realizations. Both Cardiac and respiratory motions introduce blurring in the PET parametric images if the motion is not corrected. Conventional Cardiac gating is limited by high noise level on parametric images. Dual Cardiac and respiratory gating further increases the noise level. In contrast to GA, the MR-based MC method reduces motion blurring in parametric images without increasing noise level. It also improves the myocardial defect delineation as compared to NMC method. Finally, the MR-based MC method yields lower bias and variance in K1 values than NMC and GA, respectively. The reductions of K1 bias by MR-based MC are 7.7, 5.1, 15.7, and 29.9% in four selected 0.18-mL myocardial regions of interest, respectively, as compared to NMC for CRM. MR-based MC yields 85.9, 75.3, 71.8, and 95.2% less K1 standard deviation in the four regions, respectively, as compared to GA for CRM. This simulation study suggests that the MR-based motion-correction method using PET-MR greatly reduces motion blurring on parametric images and yields less K1 bias without increasing noise level.

  • direct reconstruction of parametric images in Cardiac PET imaging in vivo studies
    The Journal of Nuclear Medicine, 2016
    Co-Authors: Yoann Petibon, Yothin Rakvongthai, Georges El Fakhri, Jinsong Ouyang
    Abstract:

    150 Objectives Direct reconstruction of parametric images from PET projection data has been shown to offer superior image quality compared to the conventional indirect method, which reconstructs a dynamic series of PET images followed by pixel-wise curve fitting of time-activity-curves (TACs). The purpose of this study was to investigate the applicability of direct parametric reconstruction to in-vivo dynamic Cardiac PET studies for the purpose of quantifying myocardial blood flow. Methods Dynamic Cardiac PET studies were performed on anesthetized pigs using a Siemens Biograph mMR scanner. List-mode PET data were collected for 10min following the injection of ~100MBq 18F-Flurpiridaz, a myocardial perfusion radiotracer. Fully-3D dynamic PET sinograms were obtained by sorting the list-mode events into a series of 8×5s, 4×30s and 4×60s frames. Additionally, to assess the performance of parametric imaging in lower counts scenarios, dynamic Cardiac gated sinograms were generated for one Cardiac phase (1/8th of the total counts). The ungated and gated dynamic datasets were used to compute parametric maps using both indirect and direct reconstruction approaches. For both cases, a one-tissue compartmental kinetic model accounting for the spillover effects from the left and right ventricles (LV/RV) was used to describe the kinetics of 18F-Flurpiridaz in the myocardium for 5min after the injection. The LV (RV) TACs were obtained using a volume-of-interest (~1x1x2.5cm3) centered in the basal portion of the LV (RV). For the indirect approach, parametric images were computed by voxel-wise non-linear least-square fitting of myocardial TACs obtained following frame-by-frame fully-3D OSEM reconstruction of the dynamic sinograms. For the direct approach, parametric maps were directly reconstructed from dynamic sinograms using a penalized likelihood reconstruction algorithm which maximizes a cost function comprised of the Poisson log-likelihood term and a spatial regularization term. Maximization of the cost-function with respect to each set of parameters was achieved using a preconditioned conjugate gradient algorithm initialized with the parametric images obtained from the indirect approach [1]. The mean and standard deviation of K1 estimates in 17 Cardiac segments were compared between the two methods. Results Visually, the direct method yielded less noisy and more uniform parametric maps than the indirect method, particularly when using the Cardiac gated data. Quantitatively, both approaches yielded similar mean K1’s (indirect: 0.84min-1, direct: 0.87min-1, p>0.3) when applied to ungated dynamic data. For the gated datasets, the direct method yielded slightly higher K1’s (indirect: 0.89 min-1, direct: 0.95 min-1, p Conclusions Direct parametric reconstruction as applied to in-vivo dynamic Cardiac PET data is a promising method for producing quantitative parametric maps with better noise control. $$graphic_C14369C6-ED48-4E1E-8446-73F86DBFE01C$$

Lance K Gould - One of the best experts on this subject based on the ideXlab platform.

  • regadenoson versus dipyridamole hyperemia for Cardiac PET imaging
    Jacc-cardiovascular Imaging, 2015
    Co-Authors: Nils P Johnson, Lance K Gould
    Abstract:

    Abstract Objectives The goal of this study was to compare regadenoson and dipyridamole hyperemia for quantitative myocardial perfusion imaging. Background Regadenoson is commonly used for stress perfusion imaging. However, no study in nuclear cardiology has employed a paired design to compare quantitative hyperemic flow from regadenoson to more traditional agents such as dipyridamole. Additionally, the timing of regadenoson bolus relative to tracer administration can be expected to affect quantitative flow. Methods Subjects underwent 2 rest/stress Cardiac positron emission tomography scans using an Rb-82 generator. Each scan employed dipyridamole and a second drug in random sequence, either regadenoson according to 5 timing sequences or repeated dipyridamole. A validated retention model quantified absolute flow and coronary flow reserve. Results A total of 176 pairs compared regadenoson (126 pairs, split unevenly among 5 timing sequences) or repeated dipyridamole (50 pairs). The cohort largely had few symptoms, only risk factors, and nearly normal relative uptake images, with 8% typical angina or dyspnea, 20% manifest coronary artery disease, and a minimum quadrant average of 80% (interquartile range: 76% to 83%) on dipyridamole scans. Hyperemic flow varied among regadenoson timing sequences but showed consistently lower stress flow and coronary flow reserve compared with dipyridamole. A timing sequence most similar to the regadenoson package insert achieved about 80% of dipyridamole hyperemia, whereas further delaying radiotracer injection reached approximately 90% of dipyridamole hyperemia. Because of the small numbers of pairs for each regadenoson timing protocol and a paucity of moderate or large perfusion defects, we did not observe a difference in relative uptake. Conclusions With the standard timing protocol from the package insert, regadenoson achieved only 80% of dipyridamole hyperemia quantitatively imaged by Cardiac positron emission tomography using Rb-82. A nonstandard protocol using a more delayed radionuclide injection after the regadenoson bolus improved its effect to 90% of dipyridamole hyperemia.

  • impact of unexpected factors on quantitative myocardial perfusion and coronary flow reserve in young asymptomatic volunteers
    Jacc-cardiovascular Imaging, 2011
    Co-Authors: Stefano Sdringola, Nils P Johnson, Richard L Kirkeeide, Lance K Gould
    Abstract:

    Objectives We sought to quantify ranges of normal myocardial perfusion and flow reserve in young, asymptomatic volunteers after systematic historical and laboratory screening for unexpected factors affecting coronary flow. Background Noninvasive Cardiac positron emission tomography (PET) quantifies absolute flow and coronary flow reserve (CFR), thereby defining physiological severity of coronary artery disease for clinical studies or management. Defining “normal” coronary flow is a necessary prerequisite to its broad clinical application. Methods Volunteers aged 20 to 40 years of age without Cardiac disease or other conditions underwent rest–dipyridamole stress Cardiac PET with absolute quantitative flow measurements using Rb-82 in paired studies at least 7 days apart for reproducibility. The presence of coronary calcium, detectable blood nicotine or caffeine, dyslipidemia, and an extended family history of early clinical atherosclerosis were objectively and systematically examined for grouping subjects as true normal or not normal. Results We enrolled 125 volunteers, 107 (86%) underwent 2 PET scans. Fifty-six (45%) were classified as true normal, whereas 69 (55%) were classified as not normal. True normals had higher high-density lipoprotein and less PET scan heterogeneity. Hemodynamic responses to dipyridamole stress were similar. Rest flow was the same in both groups (0.72 ± 0.17 ml/min/g vs. 0.69 ± 0.14 ml/min/g, p = 0.164). However, stress flow (2.89 ± 0.50 ml/min/g vs. 2.63 ± 0.61 ml/min/g, p = 0.005) and CFR (4.17 ± 0.80 vs. 3.91 ± 0.86, p = 0.047) were higher in true normals. Paired studies were performed a median of 22 days (interquartile range: 15 to 39) apart. Reproducibility was improved in the true normal group. Conclusions One-half of young, asymptomatic volunteers from the community harbor unexpected factors that mildly but systematically reduce stress flow, CFR, and reproducibility. This study establishes normal ranges and reproducibility for flow and CFR as the basis for clinical applications.

  • reducing radiation dose in rest stress Cardiac PET ct by single poststress cine ct for attenuation correction quantitative validation
    The Journal of Nuclear Medicine, 2008
    Co-Authors: Lance K Gould, Nils P Johnson, Catalin Loghin, Stefano Sdringola
    Abstract:

    Cardiac PET/CT is optimized by cine CT with dedicated shift software for manual correction of attenuation–emission misregistration. Separate rest and stress CT scans incur greater radiation dose to patients than does standard helical PET/CT or ‘‘pure’’ PET using rotating rod attenuation sources. To reduce radiation dose, we tested quantitative accuracy of using a single poststress cine CT attenuation scan for reconstructing rest perfusion images to eliminate resting CT attenuation scans. Methods: A total of 250 consecutive patients underwent diagnostic rest-dipyridamole myocardial perfusion PET/CT with 82 Rb and a 16-slice PET/CT scanner using averaged cine CT attenuation data during breathing at rest and stress. After correcting for any attenuation–emission misregistration, we quantitatively compared resting perfusion images reconstructed using rest cine CT attenuation data with the same resting emission data reconstructed with poststress cine CT attenuation data. Automated software quantifying average regional quadrant activity, severity, size, and combined size and severity of perfusion defects was used for this comparison. Results: Resting perfusion images reconstructed using rest cine CT attenuation data were quantitatively comparable to resting images reconstructed with poststress cine CT attenuation data with no clinically significant differences. Twenty-five (10%) of 250 cases required shifting of stress cine CT attenuation data to achieve optimal attenuation– emission coregistration with resting perfusion data. Eliminating rest CT attenuation scans reduced CT radiation dose by 50% below rest-plus-stress cine CT protocols. Conclusion: Resting perfusion images reconstructed using poststress cine CT attenuation data are quantitatively comparable to resting images reconstructed with resting cine CT attenuation data. Eliminating the rest CT scan reduces CT radiation dose by 50%.

  • frequent diagnostic errors in Cardiac PET ct due to misregistration of ct attenuation and emission PET images a definitive analysis of causes consequences and corrections
    The Journal of Nuclear Medicine, 2007
    Co-Authors: Lance K Gould, Nils P Johnson, Catalin Loghin, Tinsu Pan, Ashrith Guha, Stefano Sdringola
    Abstract:

    Cardiac PET combined with CT is rapidly expanding despite artifactual defects and false-positive results due to misregistration of PET and CT attenuation correction data—the frequency, cause, and correction of which remain undetermined. Methods: Two hundred fifty-nine consecutive patients underwent diagnostic rest–dipyridamole myocardial perfusion PET/CT using 82Rb, a 16-slice PET/CT scanner, helical CT attenuation correction with breathing and also at end-expiratory breath-hold, and averaged cine CT data during breathing. Misregistration on superimposed PET/CT fusion images was objectively measured in millimeters and correlated with associated quantitative size and severity of PET defects. Misregistration artifacts were defined as PET defects with corresponding misregistration on helical CT-PET fusion images that resolved after correct coregistration using a repeat CT scan, cine CT averaged attenuation during normal breathing, or shifted cine CT data that coregistered with PET data. Results: Misregistration of standard helical CT PET images caused artifactual PET defects in 103 of 259 (40%) patients that were moderate to severe in 59 (23%) (P = 0.0000) and quantitatively normalized on cine or shifted cine CT PET (P = 0.0000). Quantitative misregistration was a powerful predictor of artifact size and severity (P = 0.0000), particularly for transaxial misregistration >6 mm occurring in anterior or lateral areas in 76%, in inferior areas in 16%, and at the apex in 8% of 103 artifactual defects. Conclusion: Misregistration of helical CT attenuation and PET emission images causes artifactual defects with false-positive results in 40% of patients that normalize on cine CT PET using averaged CT attenuation data during normal breathing comparable to normal breathing during PET emission scanning and shifting cine CT images to coregister visually with PET.

  • frequent diagnostic errors in Cardiac PET ct due to misregistration of ct attenuation and emission PET images a definitive analysis of causes consequences and corrections
    The Journal of Nuclear Medicine, 2007
    Co-Authors: Lance K Gould, Nils P Johnson, Catalin Loghin, Ashrith Guha, Stefano Sdringola
    Abstract:

    UNLABELLED: Cardiac PET combined with CT is rapidly expanding despite artifactual defects and false-positive results due to misregistration of PET and CT attenuation correction data-the frequency, cause, and correction of which remain undetermined. METHODS: Two hundred fifty-nine consecutive patients underwent diagnostic rest-dipyridamole myocardial perfusion PET/CT using (82)Rb, a 16-slice PET/CT scanner, helical CT attenuation correction with breathing and also at end-expiratory breath-hold, and averaged cine CT data during breathing. Misregistration on superimposed PET/CT fusion images was objectively measured in millimeters and correlated with associated quantitative size and severity of PET defects. Misregistration artifacts were defined as PET defects with corresponding misregistration on helical CT-PET fusion images that resolved after correct coregistration using a repeat CT scan, cine CT averaged attenuation during normal breathing, or shifted cine CT data that coregistered with PET data. RESULTS: Misregistration of standard helical CT PET images caused artifactual PET defects in 103 of 259 (40%) patients that were moderate to severe in 59 (23%) (P = 0.0000) and quantitatively normalized on cine or shifted cine CT PET (P = 0.0000). Quantitative misregistration was a powerful predictor of artifact size and severity (P = 0.0000), particularly for transaxial misregistration >6 mm occurring in anterior or lateral areas in 76%, in inferior areas in 16%, and at the apex in 8% of 103 artifactual defects. CONCLUSION: Misregistration of helical CT attenuation and PET emission images causes artifactual defects with false-positive results in 40% of patients that normalize on cine CT PET using averaged CT attenuation data during normal breathing comparable to normal breathing during PET emission scanning and shifting cine CT images to coregister visually with PET.

Marcelo F Di Carli - One of the best experts on this subject based on the ideXlab platform.

  • Cardiac PET perfusion prognosis risk stratification and clinical management
    Seminars in Nuclear Medicine, 2014
    Co-Authors: Sharmila Dorbala, Marcelo F Di Carli
    Abstract:

    Myocardial perfusion imaging (MPI) with PET has expanded significantly over the past decade. With the wider availability of PET scanners and the routine use of quantitative blood flow imaging, the clinical use of PET MPI is expected to increase further. PET MPI is a powerful tool to identify risk, to quantify risk, and to guide therapy in patients with known or suspected coronary artery disease. A large body of evidence supports the prognostic value of PET MPI and ejection fraction in intermediate- to high-risk subjects, in women, in obese individuals, and in post-coronary artery bypass grafting individuals. A normal perfusion study indicates low risk (

  • prognostic value of PET myocardial perfusion imaging in obese patients
    Jacc-cardiovascular Imaging, 2014
    Co-Authors: Benjamin J W Chow, Marcelo F Di Carli, Sharmila Dorbala, Michael E Merhige, Brent A Williams, Emir Veledar, James K Min, Michael J Pencina, Yeung Yam, Li Chen
    Abstract:

    Objectives This study sought to determine and compare the prognostic and incremental value of positron emission tomography (PET) in normal, overweight, and obese patients. Background Cardiac rubidium 82 (Rb-82) PET is increasingly being used for myocardial perfusion imaging (MPI). A strength of PET is its accurate attenuation correction, thereby potentially improving its diagnostic accuracy in obese patients. The prognostic value of PET in obese patients has not been well studied. Methods A total of 7,061 patients who had undergone Rb-82 PET MPI were entered into a multicenter observational registry. All patients underwent pharmacologic Rb-82 PET and were followed for Cardiac death and all-cause mortality. Based on body mass index (BMI), patients were categorized as normal ( Results A total of 6,037 patients were followed for Cardiac death (median: 2.2 years) and the mean BMI was 30.5 ± 7.4 kg/m2. A total of 169 Cardiac deaths were observed. PET MPI demonstrated independent and incremental prognostic value over BMI. Normal PET MPI conferred an excellent prognosis with very low annual Cardiac death rates in normal (0.38%), overweight (0.43%), and obese (0.15%) patients. As well, both moderately and severe obese patients with a normal PET MPI had excellent prognosis (0.20% and 0.10%, respectively). The net reclassification improvement of PET was 0.46 (95% confidence interval [CI]: 0.31 to 0.61), and appeared similar in the moderately and severe obese patients which were 0.44 (95% CI: 0.12 to 0.76) and 0.63 (95% CI: 0.27 to 0.98), respectively. Conclusions Rb-82 PET has incremental prognostic value in all patients irrespective of BMI. In the obese population, where other modalities may have reduced diagnostic accuracy, Cardiac PET appears to be a promising noninvasive modality with prognostic value.

  • Cardiac PET ct for the evaluation of known or suspected coronary artery disease
    Radiographics, 2011
    Co-Authors: Marcelo F Di Carli, Venkatesh L Murthy
    Abstract:

    Positron emission tomography (PET) is increasingly being applied in the evaluation of myocardial perfusion. Cardiac PET can be performed with an increasing variety of cyclotron- and generator-produced radiotracers. Compared with single photon emission computed tomography, PET offers lower radiation exposure, fewer artifacts, improved spatial resolution, and, most important, improved diagnostic performance. With its capacity to quantify rest-peak stress left ventricular systolic function as well as coronary flow reserve, PET is superior to other methods for the detection of multivessel coronary artery disease and, potentially, for risk stratification. Coronary artery calcium scoring may be included for further risk stratification in patients with normal perfusion imaging findings. Furthermore, PET allows quantification of absolute myocardial perfusion, which also carries substantial prognostic value. Hybrid PET-computed tomography scanners allow functional evaluation of myocardial perfusion combined with anatomic characterization of the epicardial coronary arteries, thereby offering great potential for both diagnosis and management. Additional studies to further validate the prognostic value and cost effectiveness of PET are warranted.

  • diagnostic accuracy of rubidium 82 myocardial perfusion imaging with hybrid positron emission tomography computed tomography in the detection of coronary artery disease
    Journal of the American College of Cardiology, 2007
    Co-Authors: Uchechukwu Sampson, Sharmila Dorbala, Raymond Y Kwong, Atul M Limaye, Marcelo F Di Carli
    Abstract:

    Objectives Our objective was to determine the accuracy of rubidium-82 myocardial perfusion positron emission tomography-computed tomography (PET-CT) imaging for detecting obstructive coronary artery disease (CAD). Background Hybrid PET-CT is a new noninvasive imaging modality for evaluating patients with known or suspected CAD. Methods We evaluated 64 consecutive patients with suspected CAD undergoing rest-stress rubidium-82 Cardiac PET-CT (CT was only used for attenuation correction) and coronary angiography within 7 days (range 1 to 180 days). Patients with known CAD, previous myocardial infarction, or revascularization were excluded. Thirty-eight patients with a low likelihood for CAD were also studied. Obstructive CAD was defined as ≥70% diameter stenosis on angiography. Results The mean age of the patients was 62 ± 15 years, with a body mass index of 31 ± 8 kg/m 2 . Chest pain and/or dyspnea were the predominant reasons for evaluation. Stress perfusion defects were detected in 41 of 44 patients with obstructive CAD (sensitivity 93%, 95% confidence interval [CI] 87 to 99). The specificity of PET-CT was 83% (48 of 58, 95% CI 71 to 91), and its overall diagnostic accuracy was 87% (95% CI 79 to 93). All patients with a low likelihood for CAD showed normal scans, for a normalcy rate of 100% (38 of 38, 95% CI 91 to 100). The sensitivity for detecting CAD in patients with single and multivessel (≥2 vessels) disease was 92% (22 of 24, 95% CI 74 to 99) and 95% (19 of 20, 95% CI 74 to 99), respectively. Conclusions Myocardial perfusion PET-CT affords high sensitivity and overall accuracy for detecting CAD, including patients with single-vessel disease, women, and obese patients.

  • quantitative dynamic Cardiac 82rb PET using generalized factor and compartment analyses
    The Journal of Nuclear Medicine, 2005
    Co-Authors: Georges El Fakhri, Marcelo F Di Carli, Bastien Guerin, Arkadiusz Sitek, Marie Foley Kijewski, Stephen C Moore
    Abstract:

    We have addressed 2 major challenges of 82Rb Cardiac PET, noninvasive estimation of an accurate input function and absolute quantitation of myocardial perfusion, using a generalized form of least-squares factor analysis of dynamic sequences (GFADS) and a novel compartment analysis approach. Methods: Left and right ventricular (LV+RV) time–activity curves (TACs) were generated from 10 rest/stress studies, and 30 myocardial TACs were modeled to cover a range of clinical values. Two-dimensional PET Monte Carlo simulations of the LV, RV, myocardium, and other organs were generated separately and combined using the above TACs to form 30 realistic dynamic 82Rb studies. LV and RV TACs were estimated by GFADS and used as input to a 2-compartment kinetic analysis that estimates parametric maps of myocardial tissue extraction (k1) and egress (k2), as well as LV+RV contributions (fv, rv), by orthogonal voxel grouping. In addition, 13 patients were injected with 2.22 ± 0.19 GBq (60 ± 5 mCi) of 82Rb and imaged dynamically for 6 min at rest and during dipyridamole stress. Results: In Monte Carlo simulations, GFADS yielded estimates of the 3 factors and corresponding factor images, with average errors of −4.2% ± 6.3%, 3.5% ± 4.3%, and 2.0% ± 5.5% in the LV, RV, and myocardial factor estimates, respectively. The estimates were significantly more accurate and robust to noise than those obtained using TACs based on manually drawn volumes of interest (P

Georges El Fakhri - One of the best experts on this subject based on the ideXlab platform.

  • body motion detection and correction in Cardiac PET phantom and human studies
    Medical Physics, 2019
    Co-Authors: Tao Sun, Sally Ji Who Kim, Yoann Petibon, Georges El Fakhri, Paul Kyu Han, Nathaniel M Alpert, Jinsong Ouyang
    Abstract:

    Purpose Patient body motion during a Cardiac positron emission tomography (PET) scan can severely degrade image quality. We propose and evaluate a novel method to detect, estimate, and correct body motion in Cardiac PET. Methods Our method consists of three key components: motion detection, motion estimation, and motion-compensated image reconstruction. For motion detection, we first divide PET list-mode data into 1-s bins and compute the center of mass (COM) of the coincidences' distribution in each bin. We then compute the covariance matrix within a 25-s sliding window over the COM signals inside the window. The sum of the eigenvalues of the covariance matrix is used to separate the list-mode data into "static" (i.e., body motion free) and "moving" (i.e. contaminated by body motion) frames. Each moving frame is further divided into a number of evenly spaced sub-frames (referred to as "sub-moving" frames), in which motion is assumed to be negligible. For motion estimation, we first reconstruct the data in each static and sub-moving frame using a rapid back-projection technique. We then select the longest static frame as the reference frame and estimate elastic motion transformations to the reference frame from all other static and sub-moving frames using nonrigid registration. For motion-compensated image reconstruction, we reconstruct all the list-mode data into a single image volume in the reference frame by incorporating the estimated motion transformations in the PET system matrix. We evaluated the performance of our approach in both phantom and human studies. Results Visually, the motion-corrected (MC) PET images obtained using the proposed method have better quality and fewer motion artifacts than the images reconstructed without motion correction (NMC). Quantitative analysis indicates that MC yields higher myocardium to blood pool concentration ratios. MC also yields sharper myocardium than NMC. Conclusions The proposed body motion correction method improves image quality of Cardiac PET.

  • dynamic PET imaging of myocardial glucose consumption using mr based Cardiac respiratory correction human studies
    The Journal of Nuclear Medicine, 2019
    Co-Authors: Tao Sun, Yoann Petibon, Jinsong Ouyang, Paul Kyu Han, Georges El Fakhri
    Abstract:

    177 Purpose: Motion associated respiration and Cardiac function is a well-known source of image quality degradation in Cardiac Positron Emission Tomography (PET) studies. The continuous movement of the myocardium in PET scanning introduces artifacts that alter quantification of tracer concentration in Cardiac tissues and deteriorate diagnostic quality of image. In addition to its recognized potential in clinical cardiovascular imaging a unique feature of hybrid PET/MR is its ability of providing a robust solution to the problem of motion in PET. The aim of this study was to assess the impact of MR-based Cardiac/respiratory motion correction in dynamic Cardiac PET. Methods: The motion correction method comprises of four key components: (i) Surrogate signals for the Cardiac and respiratory cycles that are acquired continuously during the dynamic PET scan and used to assign a cardiorespiratory phase index to each measured coincidence event. (ii) A deforming MR-based cardiorespiratory tissue motion model that assigns a given cardiorespiratory motion phase index to a specific 3-D motion vector field. The motion model is obtained by means of navigators, tagging and golden-angle-based radial MR acquisitions. (iii) A motion-dependent attenuation model which is generated by deforming the acquired attenuation map with the motion model. (iv) A motion-compensated PET reconstruction algorithm that incorporates the motion and attenuation models to produce a motion corrected image volume for each dynamic frame without loss of SNR. Human studies were performed to evaluate the proposed correction method. All scans were acquired on a whole-body PET-MR system (Siemens Biograph mMR). Three volunteers were recruited for the study. FDG (average radioactivity: 10 mCi) was administered intravenously and a 50-min acquisition in list mode was initiated. Dynamic PET and motion tracking MRI data were simultaneously acquired during free-breathing. Four venous blood samples were drawn at 30, 35, 40 and 45 min after tracer administration for deriving the plasma input function. The PET data for each dynamic frame were reconstructed in two ways: with the proposed MR-based motion correction (MC) method and without motion correction (NMC). Improvement in Cardiac PET image quality was assessed by quantifying the thickness of the myocardium wall as well as the myocardium contrast-to-noise ratio in a late dynamic frame. The Patlak analysis method was applied to both MC and NMC image sets to calculate voxel-wise FDG uptake rate constants (Ki) in the myocardium. Results: Fig.1a shows that for subject 1, MC images depict overall higher activity concentration, and improved resolution compared to NMC images, as evidenced by sharper myocardium wall and improved delineation of papillary muscles. Fig.1b shows box plots that quantitatively analyze the effect of motion correction on activity estimation in different regions of the myocardium. For all three subjects, the impact of MC was most significant in septum regions, where myocardium contrast-to-noise ratio increased up to 22% and wall thickness decreased up to 18% compared to the NMC images. Fig.2a shows that for subject 1, MC yielded Ki images with higher resolution and higher Ki values in the myocardium. Fig2b shows box plots that quantitatively analyze the Ki for three subjects, which increased up to 17% after MC. Conclusions: MR-based Cardiac and respiratory motion correction benefits static and dynamic FDG PET human scans. Analyses of static data indicate that motion correction produces images with higher myocardium activity concentration, lower wall thickness and improved resolution. For dynamic imaging, higher FDG consumption rates were found in the myocardium after MC for all frames. The method potentially can provide high quality images for many Cardiac PET imaging applications. This work is under support of NIH funding R01HL118261.

  • mr based motion correction for Cardiac PET parametric imaging a simulation study
    EJNMMI Physics, 2018
    Co-Authors: Yoann Petibon, Georges El Fakhri, Kui Ying, Jinsong Ouyang
    Abstract:

    Both Cardiac and respiratory motions bias the kinetic parameters measured by dynamic PET. The aim of this study was to perform a realistic positron emission tomography-magnetic resonance (PET-MR) simulation study using 4D XCAT to evaluate the impact of MR-based motion correction on the estimation of PET myocardial kinetic parameters using PET-MR. Dynamic activity distributions were obtained based on a one-tissue compartment model with realistic kinetic parameters and an arterial input function. Realistic proton density/T1/T2 values were also defined for the MRI simulation. Two types of motion patterns, Cardiac motion only (CM) and both Cardiac and respiratory motions (CRM), were generated. PET sinograms were obtained by the projection of the activity distributions. PET image for each time frame was obtained using static (ST), gated (GA), non-motion-corrected (NMC), and motion-corrected (MC) methods. Voxel-wise unweighted least squares fitting of the dynamic PET data was then performed to obtain K1 values for each study. For each study, the mean and standard deviation of K1 values were computed for four regions of interest in the myocardium across 25 noise realizations. Both Cardiac and respiratory motions introduce blurring in the PET parametric images if the motion is not corrected. Conventional Cardiac gating is limited by high noise level on parametric images. Dual Cardiac and respiratory gating further increases the noise level. In contrast to GA, the MR-based MC method reduces motion blurring in parametric images without increasing noise level. It also improves the myocardial defect delineation as compared to NMC method. Finally, the MR-based MC method yields lower bias and variance in K1 values than NMC and GA, respectively. The reductions of K1 bias by MR-based MC are 7.7, 5.1, 15.7, and 29.9% in four selected 0.18-mL myocardial regions of interest, respectively, as compared to NMC for CRM. MR-based MC yields 85.9, 75.3, 71.8, and 95.2% less K1 standard deviation in the four regions, respectively, as compared to GA for CRM. This simulation study suggests that the MR-based motion-correction method using PET-MR greatly reduces motion blurring on parametric images and yields less K1 bias without increasing noise level.

  • direct reconstruction of parametric images in Cardiac PET imaging in vivo studies
    The Journal of Nuclear Medicine, 2016
    Co-Authors: Yoann Petibon, Yothin Rakvongthai, Georges El Fakhri, Jinsong Ouyang
    Abstract:

    150 Objectives Direct reconstruction of parametric images from PET projection data has been shown to offer superior image quality compared to the conventional indirect method, which reconstructs a dynamic series of PET images followed by pixel-wise curve fitting of time-activity-curves (TACs). The purpose of this study was to investigate the applicability of direct parametric reconstruction to in-vivo dynamic Cardiac PET studies for the purpose of quantifying myocardial blood flow. Methods Dynamic Cardiac PET studies were performed on anesthetized pigs using a Siemens Biograph mMR scanner. List-mode PET data were collected for 10min following the injection of ~100MBq 18F-Flurpiridaz, a myocardial perfusion radiotracer. Fully-3D dynamic PET sinograms were obtained by sorting the list-mode events into a series of 8×5s, 4×30s and 4×60s frames. Additionally, to assess the performance of parametric imaging in lower counts scenarios, dynamic Cardiac gated sinograms were generated for one Cardiac phase (1/8th of the total counts). The ungated and gated dynamic datasets were used to compute parametric maps using both indirect and direct reconstruction approaches. For both cases, a one-tissue compartmental kinetic model accounting for the spillover effects from the left and right ventricles (LV/RV) was used to describe the kinetics of 18F-Flurpiridaz in the myocardium for 5min after the injection. The LV (RV) TACs were obtained using a volume-of-interest (~1x1x2.5cm3) centered in the basal portion of the LV (RV). For the indirect approach, parametric images were computed by voxel-wise non-linear least-square fitting of myocardial TACs obtained following frame-by-frame fully-3D OSEM reconstruction of the dynamic sinograms. For the direct approach, parametric maps were directly reconstructed from dynamic sinograms using a penalized likelihood reconstruction algorithm which maximizes a cost function comprised of the Poisson log-likelihood term and a spatial regularization term. Maximization of the cost-function with respect to each set of parameters was achieved using a preconditioned conjugate gradient algorithm initialized with the parametric images obtained from the indirect approach [1]. The mean and standard deviation of K1 estimates in 17 Cardiac segments were compared between the two methods. Results Visually, the direct method yielded less noisy and more uniform parametric maps than the indirect method, particularly when using the Cardiac gated data. Quantitatively, both approaches yielded similar mean K1’s (indirect: 0.84min-1, direct: 0.87min-1, p>0.3) when applied to ungated dynamic data. For the gated datasets, the direct method yielded slightly higher K1’s (indirect: 0.89 min-1, direct: 0.95 min-1, p Conclusions Direct parametric reconstruction as applied to in-vivo dynamic Cardiac PET data is a promising method for producing quantitative parametric maps with better noise control. $$graphic_C14369C6-ED48-4E1E-8446-73F86DBFE01C$$

  • accelerated acquisition of tagged mri for Cardiac motion correction in simultaneous PET mr phantom and patient studies
    Medical Physics, 2015
    Co-Authors: Chuan Huang, Mark A Ahlman, David A Bluemke, Yoann Petibon, Jinsong Ouyang, Timothy G Reese, Georges El Fakhri
    Abstract:

    Purpose: Degradation of image quality caused by Cardiac and respiratory motions hampers the diagnostic quality of Cardiac PET. It has been shown that improved diagnostic accuracy of myocardial defect can be achieved by tagged MR (tMR) based PET motion correction using simultaneous PET-MR. However, one major hurdle for the adoption of tMR-based PET motion correction in the PET-MR routine is the long acquisition time needed for the collection of fully sampled tMR data. In this work, the authors propose an accelerated tMR acquisition strategy using parallel imaging and/or compressed sensing and assess the impact on the tMR-based motion corrected PET using phantom and patient data. Methods: Fully sampled tMR data were acquired simultaneously with PET list-mode data on two simultaneous PET-MR scanners for a Cardiac phantom and a patient. Parallel imaging and compressed sensing were retrospectively performed by GRAPPA and kt-FOCUSS algorithms with various acceleration factors. Motion fields were estimated using nonrigid B-spline image registration from both the accelerated and fully sampled tMR images. The motion fields were incorporated into a motion corrected ordered subset expectation maximization reconstruction algorithm with motion-dependent attenuation correction. Results: Although tMR acceleration introduced image artifacts into the tMR images for both phantom and patient data,more » motion corrected PET images yielded similar image quality as those obtained using the fully sampled tMR images for low to moderate acceleration factors (<4). Quantitative analysis of myocardial defect contrast over ten independent noise realizations showed similar results. It was further observed that although the image quality of the motion corrected PET images deteriorates for high acceleration factors, the images were still superior to the images reconstructed without motion correction. Conclusions: Accelerated tMR images obtained with more than 4 times acceleration can still provide relatively accurate motion fields and yield tMR-based motion corrected PET images with similar image quality as those reconstructed using fully sampled tMR data. The reduction of tMR acquisition time makes it more compatible with routine clinical Cardiac PET-MR studies.« less