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Noto B, Roll W, Zinken L, Rischen R, Kerschke L, Evers G, Heindel W, Schäfers M, Büther F. Respiratory motion correction in F-18-FDG PET/CT impacts lymph node assessment in lung cancer patients. EJNMMI Res 2022; 12:61. [PMID: 36107357 PMCID: PMC9478021 DOI: 10.1186/s13550-022-00926-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Accepted: 08/19/2022] [Indexed: 01/19/2023] Open
Abstract
BACKGROUNDS Elastic motion correction in PET has been shown to increase image quality and quantitative measurements of PET datasets affected by respiratory motion. However, little is known on the impact of respiratory motion correction on clinical image evaluation in oncologic PET. This study evaluated the impact of motion correction on expert readers' lymph node assessment of lung cancer patients. METHODS Forty-three patients undergoing F-18-FDG PET/CT for the staging of suspected lung cancer were included. Three different PET reconstructions were investigated: non-motion-corrected ("static"), belt gating-based motion-corrected ("BG-MC") and data-driven gating-based motion-corrected ("DDG-MC"). Assessment was conducted independently by two nuclear medicine specialists blinded to the reconstruction method on a six-point scale [Formula: see text] ranging from "certainly negative" (1) to "certainly positive" (6). Differences in [Formula: see text] between reconstruction methods, accounting for variation caused by readers, were assessed by nonparametric regression analysis of longitudinal data. From [Formula: see text], a dichotomous score for N1, N2, and N3 ("negative," "positive") and a subjective certainty score were derived. SUV and metabolic tumor volumes (MTV) were compared between reconstruction methods. RESULTS BG-MC resulted in higher scores for N1 compared to static (p = 0.001), whereas DDG-MC resulted in higher scores for N2 compared to static (p = 0.016). Motion correction resulted in the migration of N1 from tumor free to metastatic on the dichotomized score, consensually for both readers, in 3/43 cases and in 2 cases for N2. SUV was significantly higher for motion-corrected PET, while MTV was significantly lower (all p < 0.003). No significant differences in the certainty scores were noted. CONCLUSIONS PET motion correction resulted in significantly higher lymph node assessment scores of expert readers. Significant effects on quantitative PET parameters were seen; however, subjective reader certainty was not improved.
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Affiliation(s)
- Benjamin Noto
- grid.16149.3b0000 0004 0551 4246Department of Nuclear Medicine, University Hospital Münster, Münster, Germany ,grid.16149.3b0000 0004 0551 4246Clinical for Radiology, University Hospital Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Wolfgang Roll
- grid.16149.3b0000 0004 0551 4246Department of Nuclear Medicine, University Hospital Münster, Münster, Germany
| | - Laura Zinken
- grid.16149.3b0000 0004 0551 4246Department of Nuclear Medicine, University Hospital Münster, Münster, Germany
| | - Robert Rischen
- grid.16149.3b0000 0004 0551 4246Clinical for Radiology, University Hospital Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany
| | - Laura Kerschke
- grid.5949.10000 0001 2172 9288Institute of Biostatistics and Clinical Research, University of Münster, Münster, Germany
| | - Georg Evers
- grid.16149.3b0000 0004 0551 4246Department of Medicine A, Hematology, Oncology and Pulmonary Medicine, University Hospital Münster, Münster, Germany
| | - Walter Heindel
- grid.16149.3b0000 0004 0551 4246Clinical for Radiology, University Hospital Münster, Albert-Schweitzer-Campus 1, 48149 Münster, Germany ,West German Cancer Centre (WTZ), Münster, Germany
| | - Michael Schäfers
- grid.16149.3b0000 0004 0551 4246Department of Nuclear Medicine, University Hospital Münster, Münster, Germany ,grid.5949.10000 0001 2172 9288European Institute for Molecular Imaging, University of Münster, Münster, Germany ,West German Cancer Centre (WTZ), Münster, Germany
| | - Florian Büther
- grid.16149.3b0000 0004 0551 4246Department of Nuclear Medicine, University Hospital Münster, Münster, Germany ,grid.5949.10000 0001 2172 9288European Institute for Molecular Imaging, University of Münster, Münster, Germany
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2
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Armstrong IS, Hayden C, Memmott MJ, Arumugam P. A preliminary evaluation of a high temporal resolution data-driven motion correction algorithm for rubidium-82 on a SiPM PET-CT system. J Nucl Cardiol 2022; 29:56-68. [PMID: 32440990 PMCID: PMC8873161 DOI: 10.1007/s12350-020-02177-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2020] [Accepted: 04/24/2020] [Indexed: 01/08/2023]
Abstract
BACKGROUND In myocardial perfusion PET, images are acquired during vasodilator stress, increasing the likelihood of intra-frame motion blurring of the heart in reconstructed static images to assess relative perfusion. This work evaluated a prototype data-driven motion correction (DDMC) algorithm designed specifically for cardiac PET. METHODS A cardiac torso phantom, with a solid defect, was scanned stationary and being manually pulled to-and-fro in the axial direction with a random motion. Non-motion-corrected (NMC) and DDMC images were reconstructed. Total perfusion deficit was measured in the defect and profiles through the cardiac insert were defined. In addition, 46 static perfusion images from 36 rubidium-82 MPI patients were selected based upon a perception of motion blurring in the images. NMC and DDMC images were reconstructed, blinded, and scored on image quality and perceived motion. RESULTS Phantom data demonstrated near-perfect recovery of myocardial wall visualization and defect quantification with DDMC compared with the stationary phantom. Quality of clinical images was NMC: 10 non-diagnostic, 31 adequate, and 5 good; DDMC images: 0 non-diagnostic, 6 adequate, and 40 good. CONCLUSION The DDMC algorithm shows great promise in rubidium MPI PET with substantial improvements in image quality and the potential to salvage images considered non-diagnostic due to significant motion blurring.
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Affiliation(s)
- Ian S Armstrong
- Nuclear Medicine, Manchester University NHS Foundation Trust, Oxford Road, Manchester, UK.
| | - Charles Hayden
- Molecular Imaging, Siemens Medical Solutions USA, Inc., Knoxville, TN, USA
| | - Matthew J Memmott
- Nuclear Medicine, Manchester University NHS Foundation Trust, Oxford Road, Manchester, UK
| | - Parthiban Arumugam
- Nuclear Medicine, Manchester University NHS Foundation Trust, Oxford Road, Manchester, UK
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3
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Lamare F, Bousse A, Thielemans K, Liu C, Merlin T, Fayad H, Visvikis D. PET respiratory motion correction: quo vadis? Phys Med Biol 2021; 67. [PMID: 34915465 DOI: 10.1088/1361-6560/ac43fc] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 12/16/2021] [Indexed: 11/12/2022]
Abstract
Positron emission tomography (PET) respiratory motion correction has been a subject of great interest for the last twenty years, prompted mainly by the development of multimodality imaging devices such as PET/computed tomography (CT) and PET/magnetic resonance imaging (MRI). PET respiratory motion correction involves a number of steps including acquisition synchronization, motion estimation and finally motion correction. The synchronization steps include the use of different external device systems or data driven approaches which have been gaining ground over the last few years. Patient specific or generic motion models using the respiratory synchronized datasets can be subsequently derived and used for correction either in the image space or within the image reconstruction process. Similar overall approaches can be considered and have been proposed for both PET/CT and PET/MRI devices. Certain variations in the case of PET/MRI include the use of MRI specific sequences for the registration of respiratory motion information. The proposed review includes a comprehensive coverage of all these areas of development in field of PET respiratory motion for different multimodality imaging devices and approaches in terms of synchronization, estimation and subsequent motion correction. Finally, a section on perspectives including the potential clinical usage of these approaches is included.
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Affiliation(s)
- Frederic Lamare
- Nuclear Medicine Department, University Hospital Centre Bordeaux Hospital Group South, ., Bordeaux, Nouvelle-Aquitaine, 33604, FRANCE
| | - Alexandre Bousse
- LaTIM, INSERM UMR1101, Université de Bretagne Occidentale, ., Brest, Bretagne, 29285, FRANCE
| | - Kris Thielemans
- University College London Institute of Nuclear Medicine, UCL Hospital, Tower 5, 235 Euston Road, London, NW1 2BU, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Chi Liu
- Department of Diagnostic Radiology, Yale University School of Medicine Department of Radiology and Biomedical Imaging, PO Box 208048, 801 Howard Avenue, New Haven, Connecticut, 06520-8042, UNITED STATES
| | - Thibaut Merlin
- LaTIM, INSERM UMR1101, Universite de Bretagne Occidentale, ., Brest, Bretagne, 29285, FRANCE
| | - Hadi Fayad
- Weill Cornell Medicine - Qatar, ., Doha, ., QATAR
| | - Dimitris Visvikis
- LaTIM, UMR1101, Universite de Bretagne Occidentale, INSERM, Brest, Bretagne, 29285, FRANCE
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4
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Madore B, Belsley G, Cheng CC, Preiswerk F, Foley Kijewski M, Wu PH, Martell LB, Pluim JPW, Di Carli M, Moore SC. Ultrasound-based sensors for respiratory motion assessment in multimodality PET imaging. Phys Med Biol 2021; 67. [PMID: 34891142 DOI: 10.1088/1361-6560/ac4213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 12/10/2021] [Indexed: 11/11/2022]
Abstract
Breathing motion can displace internal organs by up to several cm; as such, it is a primary factor limiting image quality in medical imaging. Motion can also complicate matters when trying to fuse images from different modalities, acquired at different locations and/or on different days. Currently available devices for monitoring breathing motion often do so indirectly, by detecting changes in the outline of the torso rather than the internal motion itself, and these devices are often fixed to floors, ceilings or walls, and thus cannot accompany patients from one location to another. We have developed small ultrasound-based sensors, referred to as 'organ configuration motion' (OCM) sensors, that attach to the skin and provide rich motion-sensitive information. In the present work we tested the ability of OCM sensors to enable respiratory gating during in vivo PET imaging. A motion phantom involving an FDG solution was assembled, and two cancer patients scheduled for a clinical PET/CT exam were recruited for this study. OCM signals were used to help reconstruct phantom and in vivo data into time series of motion-resolved images. As expected, the motion-resolved images captured the underlying motion. In Patient #1, a single large lesion proved to be mostly stationary through the breathing cycle. However, in Patient #2, several small lesions were mobile during breathing, and our proposed new approach captured their breathing-related displacements. In summary, a relatively inexpensive hardware solution was developed here for respiration monitoring. Because the proposed sensors attach to the skin, as opposed to walls or ceilings, they can accompany patients from one procedure to the next, potentially allowing data gathered in different places and at different times to be combined and compared in ways that account for breathing motion.
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Affiliation(s)
- Bruno Madore
- Harvard Medical School, Department of Radiology, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts, 02115, UNITED STATES
| | - Gabriela Belsley
- Oxford Centre for Clinical Magnetic Resonance Research, Radcliffe Department of Medicine, University of Oxford, Oxford, Oxford, OX3 9DU, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Cheng-Chieh Cheng
- Computer Science and Engineering, National Sun Yat-sen University, 70 Lianhai Road, Kaohsiung, 804, TAIWAN
| | - Frank Preiswerk
- Amazon Robotics, Westborough, MA, USA, Amazon Robotics, 50 Otis St, Westborough, Massachusetts, 01581, UNITED STATES
| | - Marie Foley Kijewski
- Harvard Medical School, Department of Radiology, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts, 02115, UNITED STATES
| | - Pei-Hsin Wu
- Electrical Engineering, National Sun Yat-sen University, 70 Lianhai Road, Kaohsiung, 804, TAIWAN
| | - Laurel B Martell
- Department of Radiology, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts, 02115, UNITED STATES
| | - Josien P W Pluim
- Department of Biomedical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, Eindhoven, PO Box 513, NETHERLANDS
| | - Marcelo Di Carli
- Harvard Medical School, Department of Radiology, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts, 02115, UNITED STATES
| | - Stephen C Moore
- Department of Radiology, University of Pennsylvania Perelman School of Medicine, 3400 Civic Center Blvd, Philadelphia, Pennsylvania, 19104, UNITED STATES
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5
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Sigfridsson J, Lindström E, Iyer V, Holstensson M, Velikyan I, Sundin A, Lubberink M. Prospective data-driven respiratory gating of [ 68Ga]Ga-DOTATOC PET/CT. EJNMMI Res 2021; 11:33. [PMID: 33788025 PMCID: PMC8012445 DOI: 10.1186/s13550-021-00775-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 03/19/2021] [Indexed: 12/14/2022] Open
Abstract
Aim The aim of this prospective study was to evaluate a data-driven gating software’s performance, in terms of identifying the respiratory signal, comparing [68Ga]Ga-DOTATOC and [18F]FDG examinations. In addition, for the [68Ga]Ga-DOTATOC examinations, tracer uptake quantitation and liver lesion detectability were assessed. Methods Twenty-four patients with confirmed or suspected neuroendocrine tumours underwent whole-body [68Ga]Ga-DOTATOC PET/CT examinations. Prospective DDG was applied on all bed positions and respiratory motion correction was triggered automatically when the detected respiratory signal exceeded a certain threshold (R value ≥ 15), at which point the scan time for that bed position was doubled. These bed positions were reconstructed with quiescent period gating (QPG), retaining 50% of the total coincidences. A respiratory signal evaluation regarding the software’s efficacy in detecting respiratory motion for [68Ga]Ga-DOTATOC was conducted and compared to [18F]FDG data. Measurements of SUVmax, SUVmean, and tumour volume were performed on [68Ga]Ga-DOTATOC PET and compared between gated and non-gated images. Results The threshold of R ≥ 15 was exceeded and gating triggered on mean 2.1 bed positions per examination for [68Ga]Ga-DOTATOC as compared to 1.4 for [18F]FDG. In total, 34 tumours were evaluated in a quantitative analysis. An increase of 25.3% and 28.1%, respectively, for SUVmax (P < 0.0001) and SUVmean (P < 0.0001), and decrease of 21.1% in tumour volume (P < 0.0001) was found when DDG was applied. Conclusions High respiratory signal was exclusively detected in bed positions where respiratory motion was expected, indicating reliable performance of the DDG software on [68Ga]Ga-DOTATOC PET/CT. DDG yielded significantly higher SUVmax and SUVmean values and smaller tumour volumes, as compared to non-gated images.
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Affiliation(s)
- Jonathan Sigfridsson
- PET Centre, Uppsala University Hospital, Uppsala, Sweden. .,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.
| | - Elin Lindström
- Medical Physics, Uppsala University Hospital, Uppsala, Sweden.,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Victor Iyer
- PET Centre, Uppsala University Hospital, Uppsala, Sweden.,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Maria Holstensson
- Medical Radiation Physics and Nuclear Medicine, Karolinska University Hospital, Huddinge, Stockholm, Sweden.,Department of Clinical Science, Intervention and Technology (CLINTEC), Division of Functional Imaging and Technology, Karolinska Institute, Stockholm, Sweden
| | - Irina Velikyan
- PET Centre, Uppsala University Hospital, Uppsala, Sweden.,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Anders Sundin
- PET Centre, Uppsala University Hospital, Uppsala, Sweden.,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
| | - Mark Lubberink
- Medical Physics, Uppsala University Hospital, Uppsala, Sweden.,Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
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6
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Manwell S, Klein R, Xu T, deKemp RA. Clinical comparison of the positron emission tracking (PeTrack) algorithm with the real-time position management system for respiratory gating in cardiac positron emission tomography. Med Phys 2020; 47:1713-1726. [PMID: 31990986 DOI: 10.1002/mp.14052] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 01/09/2020] [Accepted: 01/20/2020] [Indexed: 11/11/2022] Open
Abstract
PURPOSE A data-driven motion tracking system was developed for respiratory gating in positron emission tomography (PET)/computed tomography (CT) studies. The positron emission tracking system (PeTrack) estimates the position of a low-activity fiducial marker placed on the patient during imaging. The aim of this study was to compare the performance of PeTrack against that of the real-time position management (RPM) system as applied to respiratory gating in cardiac PET/CT studies. METHODS The list-mode data of 35 patients that were referred for 82 Rb myocardial perfusion studies were retrospectively processed with PeTrack to generate respiratory motion signals and triggers. Fifty acquisitions from the initial cohort, conducted under physiologic rest and stress, were considered for analysis. Respiratory-gated reconstructions were performed using reconstruction software provided by the vendor. The respiratory signals and triggers of the gating systems were compared using quantitative measurements of the respiratory signal correlation, median, and interquartiles range (IQR) of observed respiratory rates and the relative frequencies of respiratory cycle outliers. Quantitative measurements of left-ventricular wall thicknesses and motion due to respiration were also compared. Real-time position management signals were also retrospectively processed using the trigger detection method of PeTrack for a third comparator ("RPMretro") that allowed direct comparison of the motion tracking quality independently of differences in the trigger detection methods. The comparison of PeTrack to the original RPM data represent a practical comparison of the two systems, whereas that of PeTrack and RPMretro represents an equal comparison of the two. Nongated images were also reconstructed to provide reference left-ventricular wall thicknesses. LV wall thickness and motion measurements were repeated for a subset of cases with motion ≥7 mm as image artifacts were expected to be more severe in these cases. RESULTS A significant correlation (P < 0.05) was observed between the RPM and PeTrack respiratory signals in 45/50 acquisitions; the mean correlation coefficient was 0.43. Similar results were found between PeTrack and RPMretro. No significant difference was observed between the RPM and PeTrack with respect to median respiratory rates and the percentage of respiratory cycles outliers. Respiratory rate variability (IQR) was significantly higher with PeTrack vs RPM (P = 0.002) and RPMretro (P = 0.04). Both PeTrack and RPM had a significant increase in the percentage of respiratory rate outliers compared to RPMretro (P < 0.001 and P = 0.001, respectively). All methods indicated significant differences in LV thickness compared to nongated images (P < 0.02). LV thickness was significantly larger for PeTrack compared to RPMretro in the highest motion subset (P = 0.009). Images gated with RPMretro showed significant increases in motion compared to both PeTrack (P < 0.001) and prospective RPM (P = 0.002). In the subset of highest motion cases, the difference between RPM and RPMretro was no longer present. CONCLUSIONS The data-driven PeTrack algorithm performed similarly to the well-established RPM system for respiratory gating of 82 Rb cardiac perfusion PET/CT studies. Real-time position management performance improved after retrospective processing and led to enhanced performance compared to both PeTrack and prospective RPM. With further development PeTrack has the potential to reduce the need for ancillary hardware systems to monitor respiratory motion.
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Affiliation(s)
- Spencer Manwell
- Department of Physics, Carleton University, Ottawa, Ontario, K1S 5B6, Canada.,National Cardiac PET Centre, University of Ottawa Heart Institute, Ottawa, Ontario, K1Y 4W7, Canada
| | - Ran Klein
- Department of Nuclear Medicine, The Ottawa Hospital, Ottawa, Ontario, K1H 8L6, Canada.,Division of Nuclear Medicine, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada
| | - Tong Xu
- Department of Physics, Carleton University, Ottawa, Ontario, K1S 5B6, Canada
| | - Robert A deKemp
- National Cardiac PET Centre, University of Ottawa Heart Institute, Ottawa, Ontario, K1Y 4W7, Canada
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7
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Büther F, Jones J, Seifert R, Stegger L, Schleyer P, Schäfers M. Clinical Evaluation of a Data-Driven Respiratory Gating Algorithm for Whole-Body PET with Continuous Bed Motion. J Nucl Med 2020; 61:1520-1527. [PMID: 32060218 DOI: 10.2967/jnumed.119.235770] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 01/30/2020] [Indexed: 12/13/2022] Open
Abstract
Respiratory gating is the standard to prevent respiration effects from degrading image quality in PET. Data-driven gating (DDG) using signals derived from PET raw data is a promising alternative to gating approaches requiring additional hardware (e.g., pressure-sensitive belt gating [BG]). However, continuous-bed-motion (CBM) scans require dedicated DDG approaches for axially extended PET, compared with DDG for conventional step-and-shoot scans. In this study, a CBM-capable DDG algorithm was investigated in a clinical cohort and compared with BG using optimally gated (OG) and fully motion-corrected (elastic motion correction [EMOCO]) reconstructions. Methods: Fifty-six patients with suspected malignancies in the thorax or abdomen underwent whole-body 18F-FDG CBM PET/CT using DDG and BG. Correlation analyses were performed on both gating signals. Besides static reconstructions, OG and EMOCO reconstructions were used for BG and DDG. The metabolic volume, SUVmax, and SUVmean of lesions were compared among the reconstructions. Additionally, the quality of lesion delineation in the different PET reconstructions was independently evaluated by 3 experts. Results: The global correlation coefficient between BG and DDG signals was 0.48 ± 0.11, peaking at 0.89 ± 0.07 when scanning the kidney and liver region. In total, 196 lesions were analyzed. SUV measurements were significantly higher in BG-OG, DDG-OG, BG-EMOCO, and DDG-EMOCO than in static images (P < 0.001; median SUVmax: static, 14.3 ± 13.4; BG-EMOCO, 19.8 ± 15.7; DDG-EMOCO, 20.5 ± 15.6; BG-OG, 19.6 ± 17.1; and DDG-OG, 18.9 ± 16.6). No significant differences between BG-OG and DDG-OG or between BG-EMOCO and DDG-EMOCO were found. Visual lesion delineation was significantly better in BG-EMOCO and DDG-EMOCO than in static reconstructions (P < 0.001); no significant difference was found when comparing BG and DDG for either EMOCO or OG reconstruction. Conclusion: DDG-based motion compensation of CBM PET acquisitions outperforms static reconstructions, delivering qualities comparable to BG approaches. The new algorithm may be a valuable alternative for CBM PET systems.
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Affiliation(s)
- Florian Büther
- Department of Nuclear Medicine, University Hospital Münster, Münster, Germany
| | | | - Robert Seifert
- Department of Nuclear Medicine, University Hospital Münster, Münster, Germany
| | - Lars Stegger
- Department of Nuclear Medicine, University Hospital Münster, Münster, Germany
| | | | - Michael Schäfers
- Department of Nuclear Medicine, University Hospital Münster, Münster, Germany.,European Institute for Molecular Imaging, University of Münster, Münster, Germany
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8
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Sun T, Petibon Y, Han PK, Ma C, Kim SJW, Alpert NM, El Fakhri G, Ouyang J. Body motion detection and correction in cardiac PET: Phantom and human studies. Med Phys 2019; 46:4898-4906. [PMID: 31508827 DOI: 10.1002/mp.13815] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Revised: 08/28/2019] [Accepted: 08/28/2019] [Indexed: 12/14/2022] Open
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.
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Affiliation(s)
- Tao Sun
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Yoann Petibon
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Paul K Han
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Chao Ma
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Sally J W Kim
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Nathaniel M Alpert
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Georges El Fakhri
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
| | - Jinsong Ouyang
- Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital, Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, 02115, USA
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9
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Ren S, Lu Y, Bertolli O, Thielemans K, Carson RE. Event-by-event non-rigid data-driven PET respiratory motion correction methods: comparison of principal component analysis and centroid of distribution. ACTA ACUST UNITED AC 2019; 64:165014. [DOI: 10.1088/1361-6560/ab0bc9] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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10
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Novillo F, Van Eyndhoven S, Moeyersons J, Bogaert J, Claessen G, La Gerche A, Van Huffel S, Claus P. Unsupervised respiratory signal extraction from ungated cardiac magnetic resonance imaging at rest and during exercise. Phys Med Biol 2019; 64:065001. [PMID: 30695762 DOI: 10.1088/1361-6560/ab02cd] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We propose and evaluate a method to estimate a respiratory signal from ungated cardiac magnetic resonance (CMR) images. Ungated CMR images were acquired in five subjects who performed exercise at different intensity levels under different physiological conditions while breathing freely. The respiratory motion was estimated by applying principal components analysis (PCA). A sign correction procedure was developed to correctly define inspiration and expiration, based on either tracking of the diaphragmatic motion or estimation of the lung volume or a combination of both. Evaluation was done using a plethysmograph signal as reference. There was a good correspondence between the plethysmograph and the estimated respiratory signals. Respiratory motion was effectively captured by one of the PCA components in 88% of the cases. Moreover, the proposed method successfully estimated the respiratory phase in 91% of the evaluated slices. The pipeline is robust, admitting a slight decline in performance with increased exercise intensity. Respiratory motion was accurately estimated by means of PCA and the application of a sign correction procedure. Our method showed promising results even for acquisitions during exercise where excessive body motion occurs. The proposed method provides a way to extract the respiratory signal from ungated CMR images, at rest as well as during exercise, in a fully unsupervised fashion, which may reduce the clinician's workload drastically.
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Affiliation(s)
- Felipe Novillo
- KU Leuven, Department of Cardiovascular Sciences, Cardiovascular Imaging and Dynamics, Leuven, Belgium
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11
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Gillman A, Smith J, Thomas P, Rose S, Dowson N. PET motion correction in context of integrated PET/MR: Current techniques, limitations, and future projections. Med Phys 2017; 44:e430-e445. [DOI: 10.1002/mp.12577] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 06/23/2017] [Accepted: 08/21/2017] [Indexed: 12/18/2022] Open
Affiliation(s)
- Ashley Gillman
- Australian e-Health Research Centre; CSIRO; Brisbane Australia
- Faculty of Medicine; University of Queensland; Brisbane Australia
| | - Jye Smith
- Department of Radiation Oncology; Royal Brisbane and Women's Hospital; Brisbane Australia
| | - Paul Thomas
- Faculty of Medicine; University of Queensland; Brisbane Australia
- Herston Imaging Research Facility and Specialised PET Services Queensland; Royal Brisbane and Women's Hospital; Brisbane Australia
| | - Stephen Rose
- Australian e-Health Research Centre; CSIRO; Brisbane Australia
| | - Nicholas Dowson
- Australian e-Health Research Centre; CSIRO; Brisbane Australia
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12
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Ren S, Jin X, Chan C, Jian Y, Mulnix T, Liu C, Carson RE. Data-driven event-by-event respiratory motion correction using TOF PET list-mode centroid of distribution. Phys Med Biol 2017; 62:4741-4755. [PMID: 28520558 DOI: 10.1088/1361-6560/aa700c] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Data-driven respiratory gating techniques were developed to correct for respiratory motion in PET studies, without the help of external motion tracking systems. Due to the greatly increased image noise in gated reconstructions, it is desirable to develop a data-driven event-by-event respiratory motion correction method. In this study, using the Centroid-of-distribution (COD) algorithm, we established a data-driven event-by-event respiratory motion correction technique using TOF PET list-mode data, and investigated its performance by comparing with an external system-based correction method. Ten human scans with the pancreatic β-cell tracer 18F-FP-(+)-DTBZ were employed. Data-driven respiratory motions in superior-inferior (SI) and anterior-posterior (AP) directions were first determined by computing the centroid of all radioactive events during each short time frame with further processing. The Anzai belt system was employed to record respiratory motion in all studies. COD traces in both SI and AP directions were first compared with Anzai traces by computing the Pearson correlation coefficients. Then, respiratory gated reconstructions based on either COD or Anzai traces were performed to evaluate their relative performance in capturing respiratory motion. Finally, based on correlations of displacements of organ locations in all directions and COD information, continuous 3D internal organ motion in SI and AP directions was calculated based on COD traces to guide event-by-event respiratory motion correction in the MOLAR reconstruction framework. Continuous respiratory correction results based on COD were compared with that based on Anzai, and without motion correction. Data-driven COD traces showed a good correlation with Anzai in both SI and AP directions for the majority of studies, with correlation coefficients ranging from 63% to 89%. Based on the determined respiratory displacements of pancreas between end-expiration and end-inspiration from gated reconstructions, there was no significant difference between COD-based and Anzai-based methods. Finally, data-driven COD-based event-by-event respiratory motion correction yielded comparable results to that based on Anzai respiratory traces, in terms of contrast recovery and reduced motion-induced blur. Data-driven event-by-event respiratory motion correction using COD showed significant image quality improvement compared with reconstructions with no motion correction, and gave comparable results to the Anzai-based method.
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Affiliation(s)
- Silin Ren
- Department of Biomedical Engineering, Yale University, New Haven, CT, United States of America
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13
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Yang J, Khalighi M, Hope TA, Ordovas K, Seo Y. Technical Note: Fast respiratory motion estimation using sorted singles without unlist processing: A feasibility study. Med Phys 2017; 44:1632-1637. [PMID: 28099995 DOI: 10.1002/mp.12115] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 01/10/2017] [Accepted: 01/12/2017] [Indexed: 11/09/2022] Open
Abstract
PURPOSE The study aims to demonstrate the feasibility of fast respiratory motion estimation using singles data available as a sorted format in list-mode files acquired in an integrated positron emission tomography/magnetic resonance imaging (PET/MRI) system for a proof-of-concept. METHODS The derivation of singles-driven respiratory motion (SDRM) is enabled by singles recorded and binned by second for each detector crystal in PET list-mode data acquired in a SIGNA PET/MR. The proposed method is to derive a SDRM trace by summing up all singles from all detectors through the PET data acquisition. To assess the feasibility of SDRM for data-driven gating (DDG), SDRM traces were derived from the list-mode data acquired in five liver-focused 68 Ga-DOTA-TOC PET/MRI scans, and compared with the traces derived from bellows (pressure belt). Pearson's correlation coefficients and trigger time differences at peak-inhalation phases between SDRM and bellows traces were measured for quantitative evaluation. RESULTS The method presented the average processing time of 4.2 ± 0.42 s (range: 3.9 ~ 4.7 s) for the derivation of SDRM traces. The majority of the time was spent for reading singles data from a list-mode file (3.1 ± 0.40 s, range: 2.7 ~ 3.7s). On average, the correlation coefficient of SDRM and bellows traces was 0.69 ± 0.16 (range: 0.41 ~ 0.80) and the time offset of SDRM-driven triggers from bellows-driven triggers was 0.25 ± 0.39 s (range: -0.85 ~ 2.69 s later than bellows triggers), demonstrating the similar patterns and phases of SDRM and bellows traces. CONCLUSIONS We introduced PET singles-driven respiratory motion (SDRM) estimation as a proof-of-principle, using sorted singles ready for immediate processing in list-mode data. The results demonstrated the feasibility of SDRM and its potential use for gated PET with fast processing time.
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Affiliation(s)
- Jaewon Yang
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | | | - Thomas A Hope
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA.,Department of Radiology, San Francisco VA Medical Center, San Francisco, CA, USA
| | - Karen Ordovas
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | - Youngho Seo
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA.,Joint Graduate Group in Bioengineering, University of California, San Francisco and Berkeley, CA, USA.,Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA
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14
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Mukherjee JM, Lindsay C, Mukherjee A, Olivier P, Shao L, King MA, Licho R. Improved frame-based estimation of head motion in PET brain imaging. Med Phys 2017; 43:2443. [PMID: 27147355 DOI: 10.1118/1.4946814] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Head motion during PET brain imaging can cause significant degradation of image quality. Several authors have proposed ways to compensate for PET brain motion to restore image quality and improve quantitation. Head restraints can reduce movement but are unreliable; thus the need for alternative strategies such as data-driven motion estimation or external motion tracking. Herein, the authors present a data-driven motion estimation method using a preprocessing technique that allows the usage of very short duration frames, thus reducing the intraframe motion problem commonly observed in the multiple frame acquisition method. METHODS The list mode data for PET acquisition is uniformly divided into 5-s frames and images are reconstructed without attenuation correction. Interframe motion is estimated using a 3D multiresolution registration algorithm and subsequently compensated for. For this study, the authors used 8 PET brain studies that used F-18 FDG as the tracer and contained minor or no initial motion. After reconstruction and prior to motion estimation, known motion was introduced to each frame to simulate head motion during a PET acquisition. To investigate the trade-off in motion estimation and compensation with respect to frames of different length, the authors summed 5-s frames accordingly to produce 10 and 60 s frames. Summed images generated from the motion-compensated reconstructed frames were then compared to the original PET image reconstruction without motion compensation. RESULTS The authors found that our method is able to compensate for both gradual and step-like motions using frame times as short as 5 s with a spatial accuracy of 0.2 mm on average. Complex volunteer motion involving all six degrees of freedom was estimated with lower accuracy (0.3 mm on average) than the other types investigated. Preprocessing of 5-s images was necessary for successful image registration. Since their method utilizes nonattenuation corrected frames, it is not susceptible to motion introduced between CT and PET acquisitions. CONCLUSIONS The authors have shown that they can estimate motion for frames with time intervals as short as 5 s using nonattenuation corrected reconstructed FDG PET brain images. Intraframe motion in 60-s frames causes degradation of accuracy to about 2 mm based on the motion type.
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Affiliation(s)
- J M Mukherjee
- Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
| | - C Lindsay
- Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
| | | | - P Olivier
- Philips Medical Systems, Cleveland, Ohio 44143
| | - L Shao
- ViewRay, Oakwood Village, Ohio 44146
| | - M A King
- Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
| | - R Licho
- Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
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15
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Hess M, Buther F, Schafers KP. Data-Driven Methods for the Determination of Anterior-Posterior Motion in PET. IEEE TRANSACTIONS ON MEDICAL IMAGING 2017; 36:422-432. [PMID: 27662672 DOI: 10.1109/tmi.2016.2611022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Physiological motion combined with elongated scanning times in PET leads to image degradation and quantification errors. Correction approaches usually require 1-D signals that can be obtained with hardware-based or data-driven methods. Most of the latter are optimized or limited to capture internal motion along the superior-inferior (S-I) direction. In this work we present methods for also extracting anterior-posterior (A-P) motion from PET data and propose a set of novel weighting mechanisms that can be used to emphasize certain lines-of-response (LORs) for an increased sensitivity and better signal-to-noise ratio (SNR). The proper functioning of the methods was verified in a phantom experiment. Further, their application to clinical [18F]-FDG-PET data of 72 patients revealed that using the weighting mechanisms leads to signals with significantly higher spectral respiratory weights, i.e. signals with higher quality. Information about multi-dimensional motion is contained in PET data and can be derived with data-driven methods. Motion models or correction techniques such as respiratory gating might benefit from the proposed methods as they allow to describe the three-dimensional movements of PET-positive structures more precisely.
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16
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Clinical use of quantitative cardiac perfusion PET: rationale, modalities and possible indications. Position paper of the Cardiovascular Committee of the European Association of Nuclear Medicine (EANM). Eur J Nucl Med Mol Imaging 2016; 43:1530-45. [PMID: 26846913 DOI: 10.1007/s00259-016-3317-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 01/12/2016] [Indexed: 02/06/2023]
Abstract
Until recently, PET was regarded as a luxurious way of performing myocardial perfusion scintigraphy, with excellent image quality and diagnostic capabilities that hardly justified the additional cost and procedural effort. Quantitative perfusion PET was considered a major improvement over standard qualitative imaging, because it allows the measurement of parameters not otherwise available, but for many years its use was confined to academic and research settings. In recent years, however, several factors have contributed to the renewal of interest in quantitative perfusion PET, which has become a much more readily accessible technique due to progress in hardware and the availability of dedicated and user-friendly platforms and programs. In spite of this evolution and of the growing evidence that quantitative perfusion PET can play a role in the clinical setting, there are not yet clear indications for its clinical use. Therefore, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, decided to examine the current literature on quantitative perfusion PET to (1) evaluate the rationale for its clinical use, (2) identify the main methodological requirements, (3) identify the remaining technical difficulties, (4) define the most reliable interpretation criteria, and finally (5) tentatively delineate currently acceptable and possibly appropriate clinical indications. The present position paper must be considered as a starting point aiming to promote a wider use of quantitative perfusion PET and to encourage the conception and execution of the studies needed to definitely establish its role in clinical practice.
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17
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Moody JB, Lee BC, Corbett JR, Ficaro EP, Murthy VL. Precision and accuracy of clinical quantification of myocardial blood flow by dynamic PET: A technical perspective. J Nucl Cardiol 2015; 22:935-51. [PMID: 25868451 DOI: 10.1007/s12350-015-0100-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Accepted: 02/11/2015] [Indexed: 12/23/2022]
Abstract
A number of exciting advances in PET/CT technology and improvements in methodology have recently converged to enhance the feasibility of routine clinical quantification of myocardial blood flow and flow reserve. Recent promising clinical results are pointing toward an important role for myocardial blood flow in the care of patients. Absolute blood flow quantification can be a powerful clinical tool, but its utility will depend on maintaining precision and accuracy in the face of numerous potential sources of methodological errors. Here we review recent data and highlight the impact of PET instrumentation, image reconstruction, and quantification methods, and we emphasize (82)Rb cardiac PET which currently has the widest clinical application. It will be apparent that more data are needed, particularly in relation to newer PET technologies, as well as clinical standardization of PET protocols and methods. We provide recommendations for the methodological factors considered here. At present, myocardial flow reserve appears to be remarkably robust to various methodological errors; however, with greater attention to and more detailed understanding of these sources of error, the clinical benefits of stress-only blood flow measurement may eventually be more fully realized.
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Affiliation(s)
| | | | - James R Corbett
- Division of Nuclear Medicine, Department of Radiology, University of Michigan, 1338 Cardiovascular Center, 1500 E. Medical Center Dr, SPC 5873, Ann Arbor, MI, 48109-5873, USA
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA
| | - Edward P Ficaro
- INVIA Medical Imaging Solutions, Ann Arbor, MI, USA
- Division of Nuclear Medicine, Department of Radiology, University of Michigan, 1338 Cardiovascular Center, 1500 E. Medical Center Dr, SPC 5873, Ann Arbor, MI, 48109-5873, USA
| | - Venkatesh L Murthy
- Division of Nuclear Medicine, Department of Radiology, University of Michigan, 1338 Cardiovascular Center, 1500 E. Medical Center Dr, SPC 5873, Ann Arbor, MI, 48109-5873, USA.
- Division of Cardiovascular Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA.
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18
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Kesner AL, Schleyer PJ, Büther F, Walter MA, Schäfers KP, Koo PJ. On transcending the impasse of respiratory motion correction applications in routine clinical imaging - a consideration of a fully automated data driven motion control framework. EJNMMI Phys 2014; 1:8. [PMID: 26501450 PMCID: PMC4673082 DOI: 10.1186/2197-7364-1-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2014] [Accepted: 05/23/2014] [Indexed: 12/21/2022] Open
Abstract
Positron emission tomography (PET) is increasingly used for the detection, characterization, and follow-up of tumors located in the thorax. However, patient respiratory motion presents a unique limitation that hinders the application of high-resolution PET technology for this type of imaging. Efforts to transcend this limitation have been underway for more than a decade, yet PET remains for practical considerations a modality vulnerable to motion-induced image degradation. Respiratory motion control is not employed in routine clinical operations. In this article, we take an opportunity to highlight some of the recent advancements in data-driven motion control strategies and how they may form an underpinning for what we are presenting as a fully automated data-driven motion control framework. This framework represents an alternative direction for future endeavors in motion control and can conceptually connect individual focused studies with a strategy for addressing big picture challenges and goals.
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Affiliation(s)
- Adam L Kesner
- Division of Nuclear Medicine, Department of Radiology, Anschutz Medical Campus, University of Colorado Denver, 12700 E 19th Ave, Box C-278, Aurora, CO, 80045, USA.
| | - Paul J Schleyer
- Division of Imaging Sciences and Biomedical Engineering, King's College London, London, WC2R 2LS, UK.
| | - Florian Büther
- European Institute for Molecular Imaging, University of Münster, Münster, 48149, Germany.
| | - Martin A Walter
- Institute of Nuclear Medicine and Department of Clinical Research, University Hospital Bern, Bern, 3010, Switzerland.
| | - Klaus P Schäfers
- European Institute for Molecular Imaging, University of Münster, Münster, 48149, Germany.
| | - Phillip J Koo
- Division of Nuclear Medicine, Department of Radiology, Anschutz Medical Campus, University of Colorado Denver, 12700 E 19th Ave, Box C-278, Aurora, CO, 80045, USA.
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